Trust-aware recommender system (TARS) recommends ratings based on user trust. It greatly improves the conventional collaborative filtering by providing reliable recommendations when dealing with the data sparseness problem. One basic research issue of TARS is to improve the recommending efficiency, in which the key point is to find sufficient number of recommenders efficiently for active users. Existing works searched recommenders via a skeleton, which consists of a number of hub nodes. The hub nodes are those who have superior degrees based on the scale-freeness of the trust network. However, existing works did not consider the skeleton maintenance cost and the coverage overlap between nodes of the skeleton. They also failed to suggest the proper size of the skeleton. This paper proposes an optimized TARS model to solve the problems of existing works. By using the genetic algorithm, our model chooses the most suitable nodes for the skeleton of recommender searching. It can achieve the maximum prediction coverage with the minimum skeleton maintenance cost. Simulation results show that compared with existing works, our model can reduce more than 90{\%} of the skeleton maintenance cost with reasonable prediction coverage.
Plasma endothelin-1 (ET-1) levels are elevated in spinal cord injury (SCI), and ET-1 may be involved in the pathophysiology of this condition. However, its effects on contractile function of the heart of SCI rats are still unknown. To define more clearly the possiblel role of ET-1 following SCI, we investigated the effect of ET-1 on the contraction, calcium transients and L-type calcium current (ICa,L) in the cardiomyocytes of control and SCI rats. Sixteen Sprague-Dawley male rats aged 80-100 days and weighing 250-350 g were randomized into control and SCI groups. Fourteen days following compression injury to the spinal cord, effects of ET-1 on the contraction, calcium transients and ICa,L were studied in the cardiomyocytes of control and SCI rats by the technique of simultaneous measurement of intracellular Ca2+ and contraction and by whole-cell configuration of the patch-clamp technique. In myocytes from control rats, ET-1 significantly increased contraction, the magnitude of Ca2+ transients and the peak amplitude of ICa,L. However, ET-1 had little effect on the amplitude of contraction, calcium transients and ICa,L in myocytes from SCI rats. These results suggest that the positive inotropic effects of ET-1 on control myocardial contraction may be altered in pathological states such as SCI., Y.-F. Guo ... [et al.]., and Obsahuje bibliografii a bibliografické odkazy