29,113 research outputs found
General Volume-Preserving Mechanical Systems
In this letter, we present the general form of equations that generate a
volume-preserving flow on a symplectic manifold (M, \omega). It is shown that
every volume-preserving flow has some 2-forms acting the role of the
Hamiltonian functions in the Hamiltonian mechanics and the ordinary Hamilton
equations are included as a special case with a 2-form \frac{1}{n-1} H \omega
where H is the corresponding Hamiltonian.Comment: Plain LaTeX, 13 pages, no figure
Prediction-error of Prediction Error (PPE)-based Reversible Data Hiding
This paper presents a novel reversible data hiding (RDH) algorithm for
gray-scaled images, in which the prediction-error of prediction error (PPE) of
a pixel is used to carry the secret data. In the proposed method, the pixels to
be embedded are firstly predicted with their neighboring pixels to obtain the
corresponding prediction errors (PEs). Then, by exploiting the PEs of the
neighboring pixels, the prediction of the PEs of the pixels can be determined.
And, a sorting technique based on the local complexity of a pixel is used to
collect the PPEs to generate an ordered PPE sequence so that, smaller PPEs will
be processed first for data embedding. By reversibly shifting the PPE histogram
(PPEH) with optimized parameters, the pixels corresponding to the altered PPEH
bins can be finally modified to carry the secret data. Experimental results
have implied that the proposed method can benefit from the prediction procedure
of the PEs, sorting technique as well as parameters selection, and therefore
outperform some state-of-the-art works in terms of payload-distortion
performance when applied to different images.Comment: There has no technical difference to previous versions, but rather
some minor word corrections. A 2-page summary of this paper was accepted by
ACM IH&MMSec'16 "Ongoing work session". My homepage: hzwu.github.i
Cavity-Assisted Dynamical Spin-Orbit Coupling in Cold Atoms
We consider ultracold atoms subjected to a cavity-assisted two-photon Raman
transition. The Raman coupling gives rise to effective spin-orbit interaction
which couples atom's center-of-mass motion to its pseudospin degrees of
freedom. Meanwhile, the cavity photon is dynamically affected by the atom. This
feedback between atom and photon leads to a dramatic modification of the atomic
dispersion relation, and further leads to dynamical instability of the system.
We propose to detect the change of cavity photon number as a direct way to
demonstrate dynamical instability.Comment: 5 pages, 5 figure
Synthetic Landau levels and spinor vortex matter on Haldane spherical surface with magnetic monopole
We present a flexible scheme to realize exact flat Landau levels on curved
spherical geometry in a system of spinful cold atoms. This is achieved by
Floquet engineering of a magnetic quadrupole field. We show that a synthetic
monopole field in real space can be created. We prove that the system can be
exactly mapped to the electron-monopole system on sphere, thus realizing
Haldane's spherical geometry for fractional quantum Hall physics. The scheme
works for either bosons or fermions. We investigate the ground state vortex
pattern for an -wave interacting atomic condensate by mapping this system to
the classical Thompson's problem. We further study the distortion and stability
of the vortex pattern when dipolar interaction is present. Our scheme is
compatible with current experimental setup, and may serve as a promising route
of investigating quantum Hall physics and exotic spinor vortex matter on curved
space.Comment: 11 pages, 4 figure
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