22,675 research outputs found
Quantum percolation in quantum spin Hall antidot systems
We study the influences of antidot-induced bound states on transport
properties of two- dimensional quantum spin Hall insulators. The bound
statesare found able to induce quantum percolation in the originally insulating
bulk. At some critical antidot densities, the quantum spin Hall phase can be
completely destroyed due to the maximum quantum percolation. For systems with
periodic boundaries, the maximum quantum percolationbetween the bound states
creates intermediate extended states in the bulk which is originally gapped and
insulating. The antidot in- duced bound states plays the same role as the
magnetic field inthe quantum Hall effect, both makes electrons go into
cyclotron motions. We also draw an analogy between the quantum percolation
phenomena in this system and that in the network models of quantum Hall effect
Investigation of the Finite Element Software Packages at KSC
The useful and powerful features of NASTRAN and three real world problems for the testing of the capabilities of different NASTRAN versions are discussed. The test problems involve direct transient analysis, nonlinear analysis, and static analysis. The experiences in using graphics software packages are also discussed. It was found that MSC/XL can be more useful if it can be improved to generate picture files of the analysis results and to extend its capabilities to support finite element codes other than MSC/NASTRAN. It was found that the current version of SDRC/I-DEAS (version VI) may have bugs in the module 'Data Loader'
Surface and Edge States in Topological Semi-metals
We study the topologically non-trivial semi-metals by means of the 6-band
Kane model. Existence of surface states is explicitly demonstrated by
calculating the LDOS on the material surface. In the strain free condition,
surface states are divided into two parts in the energy spectrum, one part is
in the direct gap, the other part including the crossing point of surface state
Dirac cone is submerged in the valence band. We also show how uni-axial strain
induces an insulating band gap and raises the crossing point from the valence
band into the band gap, making the system a true topological insulator. We
predict existence of helical edge states and spin Hall effect in the thin film
topological semi-metals, which could be tested with future experiment. Disorder
is found to significantly enhance the spin Hall effect in the valence band of
the thin films
What a Nerd! Beating Students and Vector Cosine in the ESL and TOEFL Datasets
In this paper, we claim that Vector Cosine, which is generally considered one
of the most efficient unsupervised measures for identifying word similarity in
Vector Space Models, can be outperformed by a completely unsupervised measure
that evaluates the extent of the intersection among the most associated
contexts of two target words, weighting such intersection according to the rank
of the shared contexts in the dependency ranked lists. This claim comes from
the hypothesis that similar words do not simply occur in similar contexts, but
they share a larger portion of their most relevant contexts compared to other
related words. To prove it, we describe and evaluate APSyn, a variant of
Average Precision that, independently of the adopted parameters, outperforms
the Vector Cosine and the co-occurrence on the ESL and TOEFL test sets. In the
best setting, APSyn reaches 0.73 accuracy on the ESL dataset and 0.70 accuracy
in the TOEFL dataset, beating therefore the non-English US college applicants
(whose average, as reported in the literature, is 64.50%) and several
state-of-the-art approaches.Comment: in LREC 201
Nonequilibrium Structure of Colloidal Dumbbells under Oscillatory Shear
We investigate the nonequilibrium behavior of dense, plastic-crystalline
suspensions of mildly anisotropic colloidal hard dumbbells under the action of
an oscillatory shear field by employing Brownian dynamics computer simulations.
In particular, we extend previous investigations, where we uncovered novel
nonequilibrium phase transitions, to other aspect ratios and to a larger
nonequilibrium parameter space, that is, a wider range of strains and shear
frequencies. We compare and discuss selected results in the context of novel
scattering and rheological experiments. Both simulations and experiments
demonstrate that the previously found transitions from the plastic crystal
phase with increasing shear strain also occur at other aspect ratios. We
explore the transition behavior in the strain-frequency phase and summarize it
in a nonequilibrium phase diagram. Additionally, the experimental rheology
results hint at a slowing down of the colloidal dynamics with higher aspect
ratio
Framework for state and unknown input estimation of linear time-varying systems
The design of unknown-input decoupled observers and filters requires the
assumption of an existence condition in the literature. This paper addresses an
unknown input filtering problem where the existence condition is not satisfied.
Instead of designing a traditional unknown input decoupled filter, a
Double-Model Adaptive Estimation approach is extended to solve the unknown
input filtering problem. It is proved that the state and the unknown inputs can
be estimated and decoupled using the extended Double-Model Adaptive Estimation
approach without satisfying the existence condition. Numerical examples are
presented in which the performance of the proposed approach is compared to
methods from literature.Comment: This paper has been accepted by Automatica. It considers unknown
input estimation or fault and disturbances estimation. Existing approaches
considers the case where the effects of fault and disturbance can be
decoupled. In our paper, we consider the case where the effects of fault and
disturbance are coupled. This approach can be easily extended to nonlinear
system
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