<p style='text-indent:20px;'>The expected present value of dividends is one of the classical stability criteria in actuarial risk theory. In this paper, we consider the two-layer <inline-formula><tex-math id="M1">\begin{document}$ (a, b) $\end{document}</tex-math></inline-formula> dividend strategy when the risk process is modeled by a spectrally negative Lévy process, such a strategy has an increasing dividend rate when the surplus exceeds level <inline-formula><tex-math id="M2">\begin{document}$ a>0 $\end{document}</tex-math></inline-formula>, and all of the excess over <inline-formula><tex-math id="M3">\begin{document}$ b>a $\end{document}</tex-math></inline-formula> as lump sum dividend payments. Using fluctuation identities and scale functions, we obtain explicit formulas for the expected net present value of dividends until ruin and the Laplace transform of the time to ruin. Finally, numerical illustrations are present to show the impacts of parameters on the expected net present value.</p>
Coccotorus beijingensis Lin et Li, 1990 belongs to Coleoptera, Curculionidae, Curculioninae, Anthonomini. It is a herbivorous insect that damages Celtis bungeana Blume (Ulmaceae) by affecting branch growth. The mitochondrial genome of C. beijingensis was sequenced and annotated to better identify C. beijingensis and related species. The total length of the C. beijingensis mitochondrial genome was 17,071 bp, contained 37 typical genes (13 protein-coding genes, two ribosomal RNA genes, 22 transfer RNA genes) and two control regions (total length: 2,292 bp). Mitochondrial genome composition, nucleotide composition and codon usage are similar to those of other sequenced Curculionidae mitogenomes. All protein-coding genes initiated with ATN and TTG codons and ended with TAA, TAG or incomplete stop codons (TA, T). In addition, analyses of pairwise genetic distances between individual PCGs in Curculionidae species showed that ATP8 was the least conserved gene, while COI was the most conserved. Twenty-one transfer RNAs had typical cloverleaf structures, while trnS1 lacked dihydrouridine (DHU) arms. ML and BI analyses, based on 13 PCGs and two rRNAs from ten species of Curculionidae, strongly support the relationships between C. beijingensis and species of the genus Anthonomus: ((An. eugenii+ An. rubi) + C. beijingensis + (An. pomorum+ An. rectirostris)) (BS = 100; PP = 1). Our phylogenetic analyses could mean that the genus Coccotorus should be sunk under Anthonomus, but more taxon sampling is needed to verify this result.
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