Range expansion caused by climate oscillations in the past probably promoted morphological radiation in a few plant groups. In this study, we aim to test this hypothesis through phylogeographical analysis of the cold-tolerant fir genus (Abies) in the Qinghai-Tibet Plateau (QTP) and Himalayas, where it comprises 12 described species. We examined sequence variation in two maternally inherited mitochondrial (mt) DNA fragments (nad5-4 and nad7-1) and two paternally inherited plastid DNA fragments (trnS-G and trnL-F) for 733 individuals from 75 populations of the species in a monophyletic group. Only six mtDNA haplotypes were recovered, but five were shared between multiple species and one occurred at a high frequency, providing strong evidence of range expansion. Forty-three plastid DNA haplotypes were detected, 19 of which were shared between species and three occurred at high frequency. Network, mismatch and Bayesian skyline plot analyses of all plastid DNA haplotypes from this clade clearly suggested range expansion. This expansion was dated as having occurred during the longest and most extensive glaciation in the Pleistocene. Our results therefore supported the range expansion hypothesis for this clade of Abies during the Pleistocene; expansion probably drove the morphological radiation of the clade in the QTP and Himalayas, although it remains unclear whether the different morphotypes should be acknowledged as independent, reproductively isolated species.
OH* and CH* chemiluminescence in hydrocarbon flames are often applied to characterize flame structure, equivalence ratio, strain rate, heat release rate, etc. In this study, chemiluminescence images of OH*, CH*, and CO 2 * in the CH 4 / O 2 diffusion flame were obtained using a CCD camera imaging system. The effect of CO 2 dilution on the flame structure, strain rate, and other flame characteristics of CH 4 /O 2 diffusion flame was discussed. The results show that CO 2 dilution greatly affects flame morphology and chemiluminescence intensity. There are quantitative functions between the chemiluminescence peak intensity of OH* and CH* and the CO 2 dilution level. The CO 2 * average intensity in the flame zone is better suited to characterize the dilution level than the CO 2 * peak intensity. Moreover, the strain rate of CO 2 -diluted laminar flame is defined. It is found that there is a linear relationship between the thickness of the OH* reaction zone and the square root of the strain rate.
Merton model has provided a classic theoretical framework for explaining credit spreads. This paper extends Merton model by introducing morphology factor of asset value volatility in the model, and conducts empirical studies on the effect of asset volatility morphology on credit spreads in China’s bond market. The results show that asset volatility morphology is economically important and can explain credit spreads well. Furthermore, this paper analyzes the asymmetric influences of monetary policy on credit spreads and asset volatility morphology. This paper points out that the responses of credit spreads and asset volatility morphology to monetary policy are consistent in the tight liquidity environments. To this end, monetary policy and liquidity, which are two factors that have been ignored by classic Merton model but proved to have significant influences on credit spreads, play roles in influencing credit spreads by changing volatility morphology of asset value. Since asset volatility morphology can reflect the change of investors’ expectation on the default probability of asset, the argument mentioned in the credit spread puzzle that the fundamentals related to bond default probability cannot explain credit spreads needs to be reexamined.
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