844 research outputs found
Effective Magnetic Fields in Graphene Superlattices
We demonstrate that the electronic spectrum of graphene in a one-dimensional
periodic potential will develop a Landau level spectrum when the potential
magnitude varies slowly in space. The effect is related to extra Dirac points
generated by the potential whose positions are sensitive to its magnitude. We
develop an effective theory that exploits a chiral symmetry in the Dirac
Hamiltonian description with a superlattice potential, to show that the low
energy theory contains an effective magnetic field. Numerical diagonalization
of the Dirac equation confirms the presence of Landau levels. Possible
consequences for transport are discussed.Comment: 4 pages (+ 2 pages of supplementary material), 3 figure
Reliable camera motion estimation from compressed MPEG videos using machine learning approach
As an important feature in characterizing video content, camera motion has been widely applied in various multimedia and computer vision applications. A novel method for fast and reliable estimation of camera motion from MPEG videos is proposed, using support vector machine for estimation in a regression model trained on a synthesized sequence. Experiments conducted on real sequences show that the proposed method yields much improved results in estimating camera motions while the difficulty in selecting valid macroblocks and motion vectors is skipped
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