2,085 research outputs found
Subjective Quality Assessment of the Impact of Buffer Size in Fine-Grain Parallel Video Encoding
Fine-Grain parallelism is essential for real-time video encoding performance. This usually implies setting a fixed buffer size for each encoded block. The choice of this parameter is critical for both performance and hardware cost. In this paper we analyze the impact of buffer size on image subjective quality, and its relation with other encoding parameters. We explore the consequences on visual quality, when minimizing buffer size to the point of causing the discard of quantized coefficients for highest frequencies. Finally, we propose some guidelines for the choice of buffer size, that has proven to be heavily dependent, in addition to other parameters, on the type of sequence being encoded. These guidelines are useful for the design of efficient realtime encoders, both hardware and software
Synthetic magnetic field effects on neutral bosonic condensates in quasi three-dimensional anisotropic layered structures
We discuss a system of dilute Bose gas confined in a layered structure of
stacked square lattices (slab geometry). A derived phase diagram reveals a
non-monotonic dependence of the ratio of tunneling to on-site repulsion on the
artificial magnetic field applied to the system. The effect is reduced when
more layers are added, which mimics a two- to quasi-three-dimensional geometry
crossover. Furthermore, we establish a correspondence between anisotropic
infinite (quasi three-dimensional) and isotropic finite (slab geometry) systems
that share exactly the same critical values, which can be an important clue for
choosing experimental setups that are less demanding, but still leading to the
identical results. Finally, we show that the properties of the ideal Bose gas
in a three-dimensional optical lattice can be closely mimicked by finite (slab)
systems, when the number of two-dimensional layers is larger than ten for
isotropic interactions or even less, when the layers are weakly coupled.Comment: http://pra.aps.org/abstract/PRA/v83/i2/e02360
Quantum rotor description of the Mott-insulator transition in the Bose-Hubbard model
We present the novel approach to the Bose-Hubbard model using the
quantum rotor description. The effective action formalism
allows us to formulate a problem in the phase only action and obtain an
analytical formulas for the critical lines. We show that the nontrivial
phase field configurations have an impact on the phase
diagrams. The topological character of the quantum field is governed by terms
of the integer charges - winding numbers. The comparison presented results to
recently obtained quantum Monte Carlo numerical calculations suggests that the
competition between quantum effects in strongly interacting boson systems is
correctly captured by our model.Comment: accepted to PR
Dissipate locally, couple globally: a sharp transition from decoupling to infinite range coupling in Josephson arrays with on-site dissipation
We study the T=0 normal to superconducting transition of Josephson arrays
with {\it on-site} dissipation. A perturbative renormalization group solution
is given. Like the previously studied case of {\it bond} dissipation (BD), this
is a "floating" to coupled (FC) phase transition. {\it Unlike} the BD
transition, at which {\it only} nearest-neighbor couplings become relevant,
here {\it all} inter-grain couplings, out to {\it infinitely} large distances,
do so simultaneously. We predict, for the first time in an FC transition, a
diverging spatial correlation length. Our results show the robustness of
floating phases in dissipative quantum systems.Comment: 7+ pages, 3 eps figures, Europhysics Letters preprint format, as
publishe
Local dissipation effects in two-dimensional quantum Josephson junction arrays with magnetic field
We study the quantum phase transitions in two-dimensional arrays of
Josephson-couples junctions with short range Josephson couplings (given by the
Josephson energy) and the charging energy. We map the problem onto the solvable
quantum generalization of the spherical model that improves over the mean-field
theory method. The arrays are placed on the top of a two-dimensional electron
gas separated by an insulator. We include effects of the local dissipation in
the presence of an external magnetic flux f in square lattice for several
rational fluxes f=0,1/2,1/3,1/4 and 1/6. We also have examined the T=0
superconducting-insulator phase boundary as function of a dissipation alpha for
two different geometry of the lattice: square and triangular. We have found
critical value of the dissipation parameter independent on geometry of the
lattice and presence magnetic field.Comment: accepted to PR
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