Parameter estimation for load-sharing system subject to Wiener degradation process using the expectation-maximization algorithm

In practice, many systems exhibit load-sharing behavior, where the surviving components share the total load imposed on the system. Different from general systems, the components of load-sharing systems are interdependent in nature, in such a way that when one component fails, the system load has to be shared by the remaining components, which increases the failure rate or degradation rate of the remaining components. Because of the load-sharing mechanism among components, parameter estimation and reliability assessment are usually complicated for load-sharing systems. Although load-sharing systems with components subject to sudden failures have been intensely studied in literatures with detailed estimation and analysis approaches, those with components subject to degradation are rarely investigated. In this paper, we propose the parameter estimation method for load-sharing systems subject to continuous degradation with a constant load. Likelihood function based on the degradation data of components is established as a first step. The maximum likelihood estimators for unknown parameters are deduced and obtained via expectation-maximization (EM) algorithm considering the nonclosed form of the likelihood function. Numerical examples are used to illustrate the effectiveness of the proposed method

Collectivity evolution in the neutron-rich Pd isotopes towards the N=82 shell closure

The neutron-rich, even-even 122,124,126Pd isotopes has been studied via in-beam gamma-ray spectroscopy at the RIKEN Radioactive Isotope Beam Factory. Excited states at 499(9), 590(11), and 686(17) keV were found in the three isotopes, which we assign to the respective 2+ -> 0+ decays. In addition, a candidate for the 4+ state at 1164(20) keV was observed in 122Pd. The resulting Ex(2+) systematics are essentially similar to those of the Xe (Z=54) isotopic chain and theoretical prediction by IBM-2, suggesting no serious shell quenching in the Pd isotopes in the vicinity of N=82

Structure of 136Sn and the Z = 50 magicity

The first 2+ excited state in the neutron-rich tin isotope 136Sn has been identified at 682(13) keV by measuring γ -rays in coincidence with the one proton removal channel from 137Sb. This value is higher than those known for heavier even-even N = 86 isotones, indicating the Z = 50 shell closure. It compares well to the first 2+ excited state of the lighter tin isotope 134Sn, which may suggest that the seniority scheme also holds for 136Sn. Our result confirms the trend of lower 2+ excitation energies of even-even tin isotopes beyond N = 82 compared to the known values in between the two doubly magic nuclei 100Sn and 132Sn. © The Author(s) 2014.published_or_final_versio

Prognostic significance of the expression of GFRα1, GFRα3 and Syndecan-3, Proteins binding ARTEMIN, In mammary carcinoma

10.1186/1471-2407-13-34BMC Cancer13-BCMA

Investigating nuclear shell structure in the vicinity of 78Ni: Low-lying excited states in the neutron-rich isotopes 80,82Zn

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