41,175 research outputs found
Superconductivity in spinel oxide LiTi2O4 epitaxial thin films
LiTi2O4 is a unique material in that it is the only known oxide spinel
superconductor. Although bulk studies have demonstrated that superconductivity
can be generally described by the Bardeen-Cooper-Schreiffer theory, the
microscopic mechanisms of superconductivity are not yet resolved fully. The
sensitivity of the superconducting properties to various defects of the spinel
crystal structure provides insight into such mechanisms. Epitaxial films of
LiTi2O4 on single crystalline substrates of MgAl2O4, MgO, and SrTiO3 provide
model systems to systematically explore the effects of lattice strain and
microstructural disorder. Lattice strain that affects bandwidth gives rise to
limited variations in the superconducting and normal state properties.
Microstructural disorder such as antiphase boundaries that give rise to Ti
network disorder can reduce the critical temperature, but Ti network disorder
combined with Mg interdiffusion can affect the superconducting state much more
dramatically. Thickness dependent transport studies indicate a
superconductor-insulator transition as a function of film thickness regardless
of lattice strain and microstructure. In addition, surface sensitive X-ray
absorption spectroscopy has identified Ti to retain site symmetry and average
valence of the bulk material regardless of film thickness.Comment: 25 pages, 7 figures, v2 - expanded Fig 1,2,7 with added discussion
Color mixing in high-energy hadron collisions
The color mixing of mesons propagating in a nucleus is studied with the help
of a color-octet Pomeron partner present in the two-gluon model of the Pomeron.
For a simple model with four meson-nucleon channels, color mixings are found to
be absent for pointlike mesons and very small for small mesons. These results
seem to validate the absorption model with two independent color components
used in recent analyses of the nuclear absorption of mesons produced
in nuclear reactions.Comment: 3 journal-style page
The role of magnetic anisotropy in spin filter junctions
We have fabricated oxide based spin filter junctions in which we demonstrate
that magnetic anisotropy can be used to tune the transport behavior of spin
filter junctions. Until recently, spin filters have been largely comprised of
polycrystalline materials where the spin filter barrier layer and one of the
electrodes are ferromagnetic. These spin filter junctions have relied on the
weak magnetic coupling between one ferromagnetic electrode and a barrier layer
or the insertion of a nonmagnetic insulating layer in between the spin filter
barrier and electrode. We have demonstrated spin filtering behavior in
La0.7Sr0.3MnO3/chromite/Fe3O4 junctions without nonmagnetic spacer layers where
the interface anisotropy plays a significant role in determining transport
behavior. Detailed studies of chemical and magnetic structure at the interfaces
indicate that abrupt changes in magnetic anisotropy across the
non-isostructural interface is the cause of the significant suppression of
junction magnetoresistance in junctions with MnCr2O4 barrier layers.Comment: 7 pages, 7 figure
20 cm VLA Radio-Continuum Study of M31 - Images and Point Source Catalogues
We present a series of new high-sensitivity and high-resolution
radio-continuum images of M31 at \lambda=20 cm (\nu=1.4 GHz). These new images
were produced by merging archived 20 cm radio-continuum observations from the
Very Large Array (VLA) telescope. Images presented here are sensitive to rms=60
\mu Jy and feature high angular resolution (<10"). A complete sample of
discrete radio sources have been catalogued and analysed across 17 individual
VLA projects. We identified a total of 864 unique discrete radio sources across
the field of M31. One of the most prominent regions in M31 is the ring feature
for which we estimated total integrated flux of 706 mJy at \lambda=20 cm. We
compare here, detected sources to those listed in Gelfand et al. (2004) at
\lambda=92 cm and find 118 sources in common to both surveys. The majority
(61%) of these sources exhibit a spectral index of \alpha <-0.6 indicating that
their emission is predominantly non-thermal in nature. That is more typical for
background objects.Comment: 28 pages, 25 figures, accepted for publication in the Serbian
Astronomical Journa
The universal functorial equivariant Lefschetz invariant
We introduce the universal functorial equivariant Lefschetz invariant for
endomorphisms of finite proper G-CW-complexes, where G is a discrete group. We
use K_0 of the category of "phi-endomorphisms of finitely generated free
RPi(G,X)-modules". We derive results about fixed points of equivariant
endomorphisms of cocompact proper smooth G-manifolds.Comment: 33 pages; shortened version of the author's PhD thesis, supervised by
Wolfgang Lueck, Westfaelische Wilhelms-Universitaet Muenster, 200
Perspective on Quark Mass and Mixing Relations
Recent data indicate that , while
seems to be GeV. The relations and suggest that %a plausible clean separation of
the %origin of the quark mixing matrix: the down type sector is responsible for
and , while comes from the up
type sector. Five to six parameters might suffice to account for the ten quark
mass and mixing parameters, resulting in specific power series representations
for the mass matrices. In this picture, seems to be the more sensible
expansion parameter, while is
tied empirically to .Comment: 10 pages, ReVtex, no figure
Countering Social Engineering through Social Media: An Enterprise Security Perspective
The increasing threat of social engineers targeting social media channels to
advance their attack effectiveness on company data has seen many organizations
introducing initiatives to better understand these vulnerabilities. This paper
examines concerns of social engineering through social media within the
enterprise and explores countermeasures undertaken to stem ensuing risk. Also
included is an analysis of existing social media security policies and
guidelines within the public and private sectors.Comment: Proceedings of The 7th International Conference on Computational
Collective Intelligence Technologies and Applications (ICCCI 2015), LNAI,
Springer, Vol. 9330, pp. 54-6
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