An improved method based on a genetic algorithm (GA) is developed to design a broadband electrical impedance matching network for piezoelectric ultrasound transducer. A key feature of the new method is that it can optimize both the topology of the matching network and perform optimization on the components. The main idea of this method is to find the optimal matching network in a set of candidate topologies. Some successful experiences of classical algorithms are absorbed to limit the size of the set of candidate topologies and greatly simplify the calculation process. Both binary-coded GA and real-coded GA are used for topology optimization and components optimization, respectively. Some calculation strategies, such as elitist strategy and clearing niche method, are adopted to make sure that the algorithm can converge to the global optimal result. Simulation and experimental results prove that matching networks with better performance might be achieved by this improved method.
The tribe Triticeae is a taxon in the Poaceae that includes several important cereal crops and forage grasses. All its species, including those that are not used for cereals or forage, are potential sources of genes for crop and forage improvement so they all have high economic value. Taxonomic treatments, including those of the Triticeae, are the basis for identification. They are often designed to reflect phylogenetic relationships and provide a guide for germplasm utilization. Traditional taxonomic treatments of the Triticeae were based on comparative morphology and geography. Morphological characters are phenotypes of an organism, resulting from interactions between or among dominant genes and environmental factors. Morphology cannot reflect recessive inheritance. Similar environmental conditions may result in morphological convergence in distantly related taxa and different environmental conditions in morphological divergence of closely related taxa. Consequently, traditional morphological taxonomy may result in misclassification. Cytogenetic and/or molecular genomic analysis may reveal such mistakes. On the basis of recent genomic investigations of the Triticeae, we have recognized 30 genera in this tribe. The taxonomic changes and genomic constitution of these genera are presented in this paper.
The correlation of co-located hydrogen masers (H-masers) is difficult to measure because their common-mode noise induced by the environment will be cancelled out during the comparison measurement. With the development of fibre-based high-precision time and frequency transfer techniques, the correlation of co-located hydrogen masers can be directly measured with the help of remote H-masers. Recently, a fibre-based frequency synchronization network was constructed in the Beijing region by connecting five H-masers from four institutions. The correlation coefficient of atomic clocks is defined and the correlation between two co-located H-masers is measured using both experimental and simulative methods. The results show that the correlation is not prominent until the averaging time is larger than ∼10 3 s; then, the coefficient grows rapidly for average times ranging from ∼10 3 s to ∼10 5 s and decreases beyond ∼10 5 s up to 5 d.
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