45,184 research outputs found
Neutrinoless decay nuclear matrix elements in an isotopic chain
We analyze nuclear matrix elements (NME) of neutrinoless double beta decay
calculated for the Cadmium isotopes. Energy density functional methods
including beyond mean field effects such as symmetry restoration and shape
mixing are used. Strong shell effects are found associated to the underlying
nuclear structure of the initial and final nuclei. Furthermore, we show that
NME for two-neutrino double beta decay evaluated in the closure approximation,
, display a constant proportionality with respect to
the Gamow-Teller part of the neutrinoless NME, . This
opens the possibility of determining the matrix
elements from Gamow-Teller strength functions. Finally, the
interconnected role of deformation, pairing, configuration mixing and shell
effects in the NMEs is discussed
The band gap problem: the accuracy of the Wien2k code confronted
This paper is a continuation of our detailed study [Phys. Rev. B 86, 195106
(2012)] of the performance of the recently proposed modified Becke-Jonhson
potential (mBJLDA) within the known Wien2k code. From the 41 semiconductors
that we have considered in our previous paper to compute the band gap value, we
selected 27 for which we found low temperature experimental data in order to
pinpoint the relative situation of the newly proposed Wien2k(mBJLDA) method as
compared to other methods in the literature. We found that the GWA gives the
most accurate predictions. The Wien2k (mBJLDA) code is slightly less precise,
in general. The Hybrid functionals are less accurate, on the overall. The GWA
is definitely the most precise existing method nowadays. In 88% of the
semiconductors considered the error was less than 10%. Both, the GWA and the
mBJLDA potential, reproduce the band gap of 15 of the 27 semiconductors
considered with a 5% error or less. An extra factor to be taken into account is
the computational cost. If one would seek for precision without taking this
factor into account, the GWA is the method to use. If one would prefer to
sacrifice a little the precision obtained against the savings in computational
cost, the empirical mBJLDA potential seems to be the appropriate method. We
include a graph that compares directly the performance of the best three
methods, according to our analysis, for each of the 27 semiconductors studied.
The situation is encouraging but the problem is not yet a closed issue.Comment: 8 pages, 1 figur
Dissipative dynamics of a particle in a vibrating periodic potential: Chaos and control
The dissipative chaotic dynamics of a particle subjected to a horizontally vibrating periodic potential is characterized theoretically and confirmed numerically in the case of an external chaos-controlling periodic excitation also acting on the particle. Theoretical predictions concerning the chaotic threshold in parameter space are deduced from the application of Melnikov's method that fully determine the chaos-control scenario. Also, the structure of diverse regularization regions in parameter space is explained theoretically with the aid of an energy analysis. It was found that the phase difference between the two periodic excitations involved plays a crucial role in the chaos-control scenario, with the particular feature that its optimal value depends upon the ratio between the damping coefficient and the excitation frequency. This constitutes a genuine feature of the chaos-control scenario associated with nonsteady potentials which is in contrast to the case of steady potentials. Additionally, we demonstrate the robustness of the chaos-control scenario against the presence of low-intensity Gaussian noise and reshaping of chaos-suppressing excitations
Prediction of jet engine parameters for control design using genetic programming
The simulation of a jet engine behavior is widely used in many different aspects of the engine development and maintenance. Achieving high quality jet engine control systems requires the iterative use of these simulations to virtually test the performance of the engine avoiding any possible damage on the real engine. Jet engine simulations involve the use of mathematical models which are complex and may not always be available. This paper introduces an approach based on Genetic Programming (GP) to model different parameters of a small engine for control design such as the Exhaust Gas Temperature (EGT). The GP approach has no knowledge of the characteristics of the engine. Instead, the model is found by the evolution of models based on past measurements of parameters such as the pump voltage. Once the model is obtained, it is used to predict the behaviour of the jet engine one step ahead. The proposed approach is successfully applied for the simulation of a Behotec j66 jet engine and the results are presented
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