72,766 research outputs found
Greedy Strategy Works for k-Center Clustering with Outliers and Coreset Construction
We study the problem of k-center clustering with outliers in arbitrary metrics and Euclidean space. Though a number of methods have been developed in the past decades, it is still quite challenging to design quality guaranteed algorithm with low complexity for this problem. Our idea is inspired by the greedy method, Gonzalez\u27s algorithm, for solving the problem of ordinary k-center clustering. Based on some novel observations, we show that this greedy strategy actually can handle k-center clustering with outliers efficiently, in terms of clustering quality and time complexity. We further show that the greedy approach yields small coreset for the problem in doubling metrics, so as to reduce the time complexity significantly. Our algorithms are easy to implement in practice. We test our method on both synthetic and real datasets. The experimental results suggest that our algorithms can achieve near optimal solutions and yield lower running times comparing with existing methods
Quantum Phase Transition in the Sub-Ohmic Spin-Boson Model: Extended Coherent-state Approach
We propose a general extended coherent state approach to the qubit (or
fermion) and multi-mode boson coupling systems. The application to the
spin-boson model with the discretization of a bosonic bath with arbitrary
continuous spectral density is described in detail, and very accurate solutions
can be obtained. The quantum phase transition in the nontrivial sub-Ohmic case
can be located by the fidelity and the order-parameter critical exponents for
the bath exponents can be correctly given by the fidelity
susceptibility, demonstrating the strength of the approach.Comment: 4 pages, 3 figure
Quantum phase transitions in coupled two-level atoms in a single-mode cavity
The dipole-coupled two-level atoms(qubits) in a single-mode resonant cavity
is studied by extended bosonic coherent states. The numerically exact solution
is presented. For finite systems, the first-order quantum phase transitions
occur at the strong interatomic interaction. Similar to the original Dicke
model, this system exhibits a second-order quantum phase transition from the
normal to the superradiant phases. Finite-size scaling for several observables,
such as the average fidelity susceptibility, the order parameter, and
concurrence are performed for different interatomic interactions. The obtained
scaling exponents suggest that interatomic interactions do not change the
universality class.Comment: 13 pages, 5 figure
Speaker-following Video Subtitles
We propose a new method for improving the presentation of subtitles in video
(e.g. TV and movies). With conventional subtitles, the viewer has to constantly
look away from the main viewing area to read the subtitles at the bottom of the
screen, which disrupts the viewing experience and causes unnecessary eyestrain.
Our method places on-screen subtitles next to the respective speakers to allow
the viewer to follow the visual content while simultaneously reading the
subtitles. We use novel identification algorithms to detect the speakers based
on audio and visual information. Then the placement of the subtitles is
determined using global optimization. A comprehensive usability study indicated
that our subtitle placement method outperformed both conventional
fixed-position subtitling and another previous dynamic subtitling method in
terms of enhancing the overall viewing experience and reducing eyestrain
Accurate numerical solution to the finite-size Dicke model
By using extended bosonic coherent states, a new technique to solve the Dicke
model exactly is proposed in the numerical sense. The accessible system size is
two orders of magnitude higher than that reported in literature. Finite-size
scaling for several observables, such as the ground-state energy, Berry phase,
and concurrence are analyzed. The existing discrepancy for the scaling exponent
of the concurrence is reconciled.Comment: 4 pages, 5 figures. Phys. Rev. A (in press, a Rapid Communication
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