98,034 research outputs found
Ab-initio calculations of spin tunneling through an indirect barrier
We use a fully relativistic layer Green's functions approach to investigate
spin-dependent tunneling through a symmetric indirect band gap barrier like
GaAs/AlAs/GaAs heterostructure along [100] direction. The method is based on
Linear Muffin Tin Orbitals and it is within the Density Functional Theory (DFT)
in the Local Density Approximation (LDA). We find that the results of our {\it
ab-initio} calculations are in good agreement with the predictions of our
previous empirical tight binding model [Phys. Rev. {\bf B}, 075313 (2006)]. In
addition we show the -dependence of the spin polarization which we did
not previously include in the model. The {\it ab-initio} calculations indicate
a strong -dependence of the transmission and the spin polarization due
to band non-parabolicity. A large window of 25-50 % spin polarization was found
for a barrier of 8 AlAs monolayers at = 0.03 . Our
calculations show clearly that the appearance of energy windows with
significant spin polarization depends mostly on the location of transmission
resonances and their corresponding zeros and not on the magnitude of the spin
splitting in the barrier.Comment: 10 pages, 3 figure
Collective flow of open and hidden charm in Au+Au collisions at = 200 GeV
We study the collective flow of open charm mesons and charmonia in Au+Au
collisions at = 200 GeV within the hadron-string-dynamics (HSD)
transport approach. The detailed studies show that the coupling of
mesons to the light hadrons leads to comparable directed and elliptic flow as
for the light mesons. This also holds approximately for mesons since
more than 50% of the final charmonia for central and mid-central collisions
stem from induced reactions in the transport calculations. The
transverse momentum spectra of mesons and 's are only very
moderately changed by the (pre-)hadronic interactions in HSD which can be
traced back to the collective flow generated by elastic interactions with the
light hadrons.Comment: 9 pages, 8 figures, Phys. Rev. C, in pres
An Enhanced Features Extractor for a Portfolio of Constraint Solvers
Recent research has shown that a single arbitrarily efficient solver can be
significantly outperformed by a portfolio of possibly slower on-average
solvers. The solver selection is usually done by means of (un)supervised
learning techniques which exploit features extracted from the problem
specification. In this paper we present an useful and flexible framework that
is able to extract an extensive set of features from a Constraint
(Satisfaction/Optimization) Problem defined in possibly different modeling
languages: MiniZinc, FlatZinc or XCSP. We also report some empirical results
showing that the performances that can be obtained using these features are
effective and competitive with state of the art CSP portfolio techniques
Maximum Resilience of Artificial Neural Networks
The deployment of Artificial Neural Networks (ANNs) in safety-critical
applications poses a number of new verification and certification challenges.
In particular, for ANN-enabled self-driving vehicles it is important to
establish properties about the resilience of ANNs to noisy or even maliciously
manipulated sensory input. We are addressing these challenges by defining
resilience properties of ANN-based classifiers as the maximal amount of input
or sensor perturbation which is still tolerated. This problem of computing
maximal perturbation bounds for ANNs is then reduced to solving mixed integer
optimization problems (MIP). A number of MIP encoding heuristics are developed
for drastically reducing MIP-solver runtimes, and using parallelization of
MIP-solvers results in an almost linear speed-up in the number (up to a certain
limit) of computing cores in our experiments. We demonstrate the effectiveness
and scalability of our approach by means of computing maximal resilience bounds
for a number of ANN benchmark sets ranging from typical image recognition
scenarios to the autonomous maneuvering of robots.Comment: Timestamp research work conducted in the project. version 2: fix some
typos, rephrase the definition, and add some more existing wor
Integer quantum Hall effect and topological phase transitions in silicene
We numerically investigate the effects of disorder on the quantum Hall effect
(QHE) and the quantum phase transitions in silicene based on a lattice model.
It is shown that for a clean sample, silicene exhibits an unconventional QHE
near the band center, with plateaus developing at and
a conventional QHE near the band edges. In the presence of disorder, the Hall
plateaus can be destroyed through the float-up of extended levels toward the
band center, in which higher plateaus disappear first. However, the center
Hall plateau is more sensitive to disorder and disappears at a
relatively weak disorder strength. Moreover, the combination of an electric
field and the intrinsic spin-orbit interaction (SOI) can lead to quantum phase
transitions from a topological insulator to a band insulator at the charge
neutrality point (CNP), accompanied by additional quantum Hall conductivity
plateaus.Comment: 7 pages, 4 figure
- …