425 research outputs found
Characterization and Efficient Search of Non-Elementary Trapping Sets of LDPC Codes with Applications to Stopping Sets
In this paper, we propose a characterization for non-elementary trapping sets
(NETSs) of low-density parity-check (LDPC) codes. The characterization is based
on viewing a NETS as a hierarchy of embedded graphs starting from an ETS. The
characterization corresponds to an efficient search algorithm that under
certain conditions is exhaustive. As an application of the proposed
characterization/search, we obtain lower and upper bounds on the stopping
distance of LDPC codes.
We examine a large number of regular and irregular LDPC codes, and
demonstrate the efficiency and versatility of our technique in finding lower
and upper bounds on, and in many cases the exact value of, . Finding
, or establishing search-based lower or upper bounds, for many of the
examined codes are out of the reach of any existing algorithm
Collapse and dispersal of a homogeneous spin fluid in Einstein-Cartan theory
In the present work, we revisit the process of gravitational collapse of a
spherically symmetric homogeneous dust fluid which is known as the
Oppenheimer-Snyder (OS) model [1]. We show that such a scenario would not end
in a spacetime singularity when the spin degrees of freedom of fermionic
particles within the collapsing cloud are taken into account. To this purpose,
we take the matter content of the stellar object as a homogeneous Weyssenhoff
fluid which is a generalization of perfect fluid in general relativity (GR) to
include the spin of matter. Employing the homogeneous and isotropic FLRW metric
for the interior spacetime setup, it is shown that the spin of matter, in the
context of a negative pressure, acts against the pull of gravity and
decelerates the dynamical evolution of the collapse in its later stages. Our
results bode a picture of gravitational collapse in which the collapse process
halts at a finite radius whose value depends on the initial configuration. We
thus show that the spacetime singularity that occurs in the OS model is
replaced by a non-singular bounce beyond which the collapsing cloud re-expands
to infinity. Depending on the model parameters, one can find a minimum value
for the boundary of the collapsing cloud or correspondingly a threshold value
for the mass content below which the horizon formation can be avoided. Our
results are supported by a thorough numerical analysis.Comment: 16 pages, 5 figures, revised versio
Involutive Bases Algorithm Incorporating F5 Criterion
Faugere's F5 algorithm is the fastest known algorithm to compute Groebner
bases. It has a signature-based and an incremental structure that allow to
apply the F5 criterion for deletion of unnecessary reductions. In this paper,
we present an involutive completion algorithm which outputs a minimal
involutive basis. Our completion algorithm has a nonincremental structure and
in addition to the involutive form of Buchberger's criteria it applies the F5
criterion whenever this criterion is applicable in the course of completion to
involution. In doing so, we use the G2V form of the F5 criterion developed by
Gao, Guan and Volny IV. To compare the proposed algorithm, via a set of
benchmarks, with the Gerdt-Blinkov involutive algorithm (which does not apply
the F5 criterion) we use implementations of both algorithms done on the same
platform in Maple.Comment: 24 pages, 2 figure
Load Balancing Algorithms in Cloud Computing Analysis and Performance Evaluation
Distributing the system workload and balancing all incoming requests among all processing nodes in cloud computing environments is one of the important challenges in today cloud computing world. Many load balancing algorithms and approaches have been proposed for distributed and cloud computing systems. In addition the broker policy for distributing the workload among different datacenters in a cloud environment is one of the important factors for improving the system performance. In this paper we present an analytical comparison for the combinations of VM load balancing algorithms and different broker policies. We evaluate these approaches by simulating on CloudAnalyst simulator and the final results are presented based on different parameters. The results of this research specify the best possible combinations
Design of Intelligent PID Controller for AVR System Using an Adaptive Neuro Fuzzy Inference System
This paper presents a hybrid approach involving signal to noise ratio (SNR) and particle swarm optimization (PSO) for design the optimal and intelligent proportional-integral-derivative (PID) controller of an automatic voltage regulator (AVR) system with uses an adaptive neuro fuzzy inference system (ANFIS). In this paper determined optimal parameters of PID controller with SNR-PSO approach for some events and use these optimal parameters of PID controller for design the intelligent PID controller for AVR system with ANFIS. Trial and error method can be used to find a suitable design of anfis based an intelligent controller. However, there are many options including fuzzy rules, Membership Functions (MFs) and scaling factors to achieve a desired performance. An optimization algorithm facilitates this process and finds an optimal design to provide a desired performance. This paper presents a novel application of the SNRPSO approach to design an intelligent controller for AVR. SNR-PSO is a method that combines the features of PSO and SNR in order to improve the optimize operation. In order to emphasize the advantages of the proposed SNR-PSO PID controller, we also compared with the CRPSO PID controller. The proposed method was indeed more efficient and robust in improving the step response of an AVR system and numerical simulations are provided to verify the effectiveness and feasibility of PID controller of AVR based on SNRPSO algorithm.DOI:http://dx.doi.org/10.11591/ijece.v4i5.652
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