1,691 research outputs found
Encoding for the Blackwell Channel with Reinforced Belief Propagation
A key idea in coding for the broadcast channel (BC) is binning, in which the
transmitter encode information by selecting a codeword from an appropriate bin
(the messages are thus the bin indexes). This selection is normally done by
solving an appropriate (possibly difficult) combinatorial problem. Recently it
has been shown that binning for the Blackwell channel --a particular BC-- can
be done by iterative schemes based on Survey Propagation (SP). This method uses
decimation for SP and suffers a complexity of O(n^2). In this paper we propose
a new variation of the Belief Propagation (BP) algorithm, named Reinforced BP
algorithm, that turns BP into a solver. Our simulations show that this new
algorithm has complexity O(n log n). Using this new algorithm together with a
non-linear coding scheme, we can efficiently achieve rates close to the border
of the capacity region of the Blackwell channel.Comment: 5 pages, 8 figures, submitted to ISIT 200
Momentum-space analysis of multipartite entanglement at quantum phase transitions
We investigate entanglement properties at quantum phase transitions of an
integrable extended Hubbard model in the momentum space representation. Two
elementary subsystems are recognized: the single mode of an electron, and the
pair of modes (electrons coupled through the eta-pairing mechanism). We first
detect the two/multi-partite nature of each quantum phase transition by a
comparative study of the singularities of Von Neumann entropy and quantum
mutual information. We establish the existing relations between the
correlations in the momentum representation and those exhibited in the
complementary picture: the direct lattice representation. The presence of
multipartite entanglement is then investigated in detail through the Q-measure,
namely a generalization of the Meyer-Wallach measure of entanglement. Such a
measure becomes increasingly sensitive to correlations of a multipartite nature
increasing the size of the reduced density matrix. In momentum space, we
succeed in obtaining the latter for our system at arbitrary size and we relate
its behaviour to the nature of the various QPTs.Comment: 8 pages, 4 figure
VLSI Implementation of a Non-Binary Decoder Based on the Analog Digital Belief Propagation
This work presents the VLSI hardware implementation
of a novel Belief Propagation (BP) algorithm introduced
in [1] and named as Analog Digital Belief Propagation
(ADBP). The ADBP algorithm works on factor graphs over
linear models and uses messages in the form of Gaussian
like probability distributions by tracking their parameters. In
particular, ADBP can deal with system variables that are discrete
and/or wrapped. A variant of ADBP can then be applied
for the iterative decoding of a particular class of non binary
codes and yields decoders with complexity independent of
alphabet size M, thus allowing to construct ecient decoders
for digital transmission systems with unbounded spectral
eciency. In this work, we propose some simplifications to
the updating rules for ADBP algorithm that are suitable for
hardware implementation. In addition, we analyze the eect
of finite precision on the decoding performance of the algorithm.
A careful selection of quantization scheme for input,
output and intermediate variables allows us to construct a
complete ADBP decoding architecture that performs close to
the double precision implementation and shows a promising
complexity for large values of M. Finally, synthesis results
of the main processing elements of ADBP are reported for
45 nm standard cell ASIC technology
Classical realization of two-site Fermi-Hubbard systems
A classical wave optics realization of the two-site Hubbard model, describing
the dynamics of interacting fermions in a double-well potential, is proposed
based on light transport in evanescently-coupled optical waveguides.Comment: 4 page
A Computation Fluid Dynamics Methodology for the Analysis of the Slipper-Swash Plate Dynamic Interaction in Axial Piston Pumps
This paper proposes a CFD methodology for the simulation of the slipper's dynamics of a swash-plate axial piston unit under actual operating conditions. The study considers a typical slipper design, including a vented groove at the swash-plate interface. The dynamic fluid-body interaction (DFBI) model is exploited to find the instantaneous position of the slipper, while the morphing approach is adopted to cope with the corresponding mesh distortion. A modular approach is adopted to ensure high-quality mesh on the entire slipper surface and sliding interfaces provide the fluid dynamic connection between neighboring regions. The external forces acting on the slipper are included by means of user-defined lookup tables with the simulation estimating the lift force induced by fluid compression. Moreover, the force produced by the metal-to-metal contact between the slipper and the swash plate is modeled through a specific tool of the software. The pressure signal over an entire revolution of the pump is taken as an input of the simulation and a variable time step is used to manage the high-pressure gradients occurring in the regions of inner and outer dead points of the piston. The weakly compressible characteristic of the fluid is considered by a specific pressure-dependent density approach, and the two-equation eddy-viscosity k-omega SST (shear stress transport) model is used to assess the turbulent behavior of the flow. Furthermore, the transitional model predicts the onset of transition, thus solving different equations depending on whether the flow enters a laminar or turbulent regime. In conclusion, the proposed methodology investigates the motion of the slipper in response to several external forces acting on the component. The numerical results are discussed in terms of variable clearance height, pressure distribution within the gap, and lift forces acting on the slipper under specific pump operations
Band and filling controlled transitions in exactly solved electronic models
We describe a general method to study the ground state phase diagram of
electronic models on chains whose extended Hubbard hamiltonian is formed by a
generalized permutator plus a band-controlling term. The method, based on the
appropriate interpretation of Sutherland's species, yields under described
conditions a reduction of the effective Hilbert space. In particular, we derive
the phase diagrams of two new models; the first one exhibits a band-controlled
insulator-superconductor transition at half-filling for the unusually high
value ; the second one is characterized by a filling-controlled
metal-insulator transition between two finite regions of the diagram.Comment: 5 pages, REVTEX, 2 eps figure
Spin picture of the one-dimensional Hubbard model: Two-fluid structure and phase dynamics
We propose a scheme for investigating the quantum dynamics of interacting
electron models by means of time-dependent variational principle and spin
coherent states of space lattice operators. We apply such a scheme to the
one-dimensional hubbard model, and solve the resulting equations in different
regimes. In particular, we find that at low densities the dynamics is mapped
into two coupled nonlinear Schroedinger equations, whereas near half-filling
the model is described by two coupled Josephson junction arrays. Focusing then
to the case in which only the phases of the spin variables are dynamically
active, we examine a number of different solutions corresponding to the
excitations of few macroscopic modes. Based on fixed point equation of the
simpler among them, we show that the standard one-band ground state phase space
is found.Comment: 10 pages, 1 figure, to appear on Phys. Rev.
Soft-output decoding algorithms in iterative decoding of turbo codes
In this article, we present two versions of a simplified maximum a posteriori decoding algorithm. The algorithms work in a sliding window form, like the Viterbi algorithm, and can thus be used to decode continuously transmitted sequences obtained by parallel concatenated codes, without requiring code trellis termination. A heuristic explanation is also given of how to embed the maximum a posteriori algorithms into the iterative decoding of parallel concatenated codes (turbo codes). The performances of the two algorithms are compared on the basis of a powerful rate 1/3 parallel concatenated code. Basic circuits to implement the simplified a posteriori decoding algorithm using lookup tables, and two further approximations (linear and threshold), with a very small penalty, to eliminate the need for lookup tables are proposed
A lumped parameter and CFD combined approach for the lubrication analysis of a helical gear transmission
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