30,564 research outputs found
Multi-feed cone Cassegrain antenna Patent
Design and operation of multi-feed cone Cassegrain antenn
Ab initio studies of the spin-transfer torque in tunnel junctions
We calculate the spin-transfer torque in Fe/MgO/Fe tunnel junctions and
compare the results to those for all-metallic junctions. We show that the
spin-transfer torque is interfacial in the ferromagnetic layer to a greater
degree than in all-metallic junctions. This result originates in the half
metallic behavior of Fe for the states at the Brillouin zone center;
in contrast to all-metallic structures, dephasing does not play an important
role. We further show that it is possible to get a component of the torque that
is out of the plane of the magnetizations and that is linear in the bias.
However, observation of such a torque requires highly ideal samples. In samples
with typical interfacial roughness, the torque is similar to that in
all-metallic multilayers, although for different reasons.Comment: 5 pages, 4 figure
Different steady states for spin currents in noncollinear multilayers
We find there are at least two different steady states for transport across
noncollinear magnetic multilayers. In the conventional one there is a
discontinuity in the spin current across the interfaces which has been
identified as the source of current induced magnetic reversal; in the one
advocated herein the spin torque arises from the spin accumulation transverse
to the magnetization of a magnetic layer. These two states have quite different
attributes which should be discerned by current experiments.Comment: 8 pages, no figure. Accepted for publication in Journal of Physics:
Condensed Matte
AdS-Carroll Branes
Coset methods are used to determine the action of a co-dimension one brane
(domain wall) embedded in (d+1)-dimensional AdS space in the Carroll limit in
which the speed of light goes to zero. The action is invariant under the
non-linearly realized symmetries of the AdS-Carroll spacetime. The
Nambu-Goldstone field exhibits a static spatial distribution for the brane with
a time varying momentum density related to the brane's spatial shape as well as
the AdS-C geometry. The AdS-C vector field dual theory is obtained.Comment: 47 page
Fast Matrix Factorization for Online Recommendation with Implicit Feedback
This paper contributes improvements on both the effectiveness and efficiency
of Matrix Factorization (MF) methods for implicit feedback. We highlight two
critical issues of existing works. First, due to the large space of unobserved
feedback, most existing works resort to assign a uniform weight to the missing
data to reduce computational complexity. However, such a uniform assumption is
invalid in real-world settings. Second, most methods are also designed in an
offline setting and fail to keep up with the dynamic nature of online data. We
address the above two issues in learning MF models from implicit feedback. We
first propose to weight the missing data based on item popularity, which is
more effective and flexible than the uniform-weight assumption. However, such a
non-uniform weighting poses efficiency challenge in learning the model. To
address this, we specifically design a new learning algorithm based on the
element-wise Alternating Least Squares (eALS) technique, for efficiently
optimizing a MF model with variably-weighted missing data. We exploit this
efficiency to then seamlessly devise an incremental update strategy that
instantly refreshes a MF model given new feedback. Through comprehensive
experiments on two public datasets in both offline and online protocols, we
show that our eALS method consistently outperforms state-of-the-art implicit MF
methods. Our implementation is available at
https://github.com/hexiangnan/sigir16-eals.Comment: 10 pages, 8 figure
Adiabatic connection at negative coupling strengths
The adiabatic connection of density functional theory (DFT) for electronic
systems is generalized here to negative values of the coupling strength
(with {\em attractive} electrons). In the extreme limit
a simple physical solution is presented and its implications
for DFT (as well as its limitations) are discussed. For two-electron systems (a
case in which the present solution can be calculated exactly), we find that an
interpolation between the limit and the opposite limit of
infinitely strong repulsion () yields a rather accurate
estimate of the second-order correlation energy E\cor\glt[\rho] for several
different densities , without using virtual orbitals. The same procedure
is also applied to the Be isoelectronic series, analyzing the effects of
near-degeneracy.Comment: 9 pages, submitted to PR
Subharmonic gap structure in short ballistic graphene junctions
We present a theoretical analysis of the current-voltage characteristics of a
ballistic superconductor-normal-superconductor (SNS) junction, in which a strip
of graphene is coupled to two superconducting electrodes. We focus in the
short-junction regime, where the length of the strip is much smaller than
superconducting coherence length. We show that the differential conductance
exhibits a very rich subharmonic gap structure which can be modulated by means
of a gate voltage. On approaching the Dirac point the conductance normalized by
the normal-state conductance is identical to that of a short diffusive SNS
junction.Comment: revtex4, 4 pages, 4 figure
Quadrupole Moments of Neutron-Deficient Na
The electric-quadrupole coupling constant of the ground states of the proton
drip line nucleus Na( = 2, = 447.9 ms) and the
neutron-deficient nucleus Na( = 3/2, = 22.49 s)
in a hexagonal ZnO single crystal were precisely measured to be kHz and 939 14 kHz, respectively, using the multi-frequency
-ray detecting nuclear magnetic resonance technique under presence of an
electric-quadrupole interaction. A electric-quadrupole coupling constant of
Na in the ZnO crystal was also measured to be
kHz. The electric-quadrupole moments were extracted as Na) = 10.3
0.8 fm and Na) = 14.0 1.1 fm, using
the electric-coupling constant of Na and the known quadrupole moment of
this nucleus as references. The present results are well explained by
shell-model calculations in the full -shell model space.Comment: Accepted for publication in Physics Letters
Constraints on gravity: An evidence against the covariant resolution of the Pioneer anomaly
We consider corrections in the form of to the
Einstein-Hilbert Lagrangian. Then we compute the corrections to the
Schwarszchild geometry due to the inclusion of this general term to the
Lagrangian. We show that
gives rise to a constant anomalous acceleration for objects orbiting the Sun
onward the Sun. This leads to the conclusion that would have covariantly
resolved the Pioneer anomaly if this value of had not
contradicted other observations.
We notice that the experimental bounds on grows stronger in case
we examine the deformation of the space-time geometry around objects lighter
than the Sun. We therefore use the high precision measurements around the Earth
(LAGEOS and LLR) and obtain a very strong constraint on the corrections in the
form of and in particular . This bound requires
.
Therefore it refutes the covariant resolution of the Pioneer anomaly.Comment: ...v5: references added, new discussions adde
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