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Impending climate warming is expected to influence plant growth and distribution, and the distribution range limit of tree species is extremely sensitive to climate change. However, synchronous comparisons of responses of different tree species with overlapping ecological niches to climate at their distribution range limit in the same region have received little attention. In the present study, we assessed the discrepancy in radial growth responses of two dominant oak species to climate at their distribution range limit (southern range limit for Quercus mongolica, northern range limit for Quercus variabilis) in Beijing, China. Furthermore, growth–climate relationships were examined using linear mixed‐effects models, and growth trends up to the year 2100 were forecast based on future climate scenarios (RCP2.6 and RCP8.5). Our results indicated that there were no significant differences in the growth response to climate between Q. variabilis at its northern limit and Q. mongolica at its southern limit, and the growth of the two tree species was positively correlated with the minimum temperature and negatively correlated with the climatic moisture deficit of autumn. However, the growth response to climate variables varied at different sites. Additionally, the model forecast showed an increase in radial growth of Q. variabilis at its northern limit and Q. mongolica at its southern limit up to the end of the present century.

Cerasus dielsiana (Rosaceae) is one of the most characteristic wild flowering cherry species endemic to subtropical China, with high conservation value from ornamental, economic, and ecological perspectives. To verify its spatial genetic structure and phylogeographic history, evaluation of nuclear (ITS) sequence variation in 203 individuals from 25 wild populations across its natural distribution ranges was conducted. High levels of ribotypes and nuclear diversity (Hd = 0.879 ± 0.012, π = 3.56 ± 0.16) were detected at the species level. Spatial analysis of molecular variation (SAMOVA), median-joining network and phylogenetic Neighbour-joining tree assigned the populations into four genetically distinct groups. Meanwhile, high levels of genetic differentiation among populations and strong phylogeographic patterns (Nst = 0.837 > Gst = 0.585; P C. dielsiana, and at least three potential in situ glacial refugia as well as recent demographic expansion in eastern region have been detected. Collectively, we highlight that the combined effect of natural selection and random genetic drift under complex topography and palaeoclimatic oscillations since the Last Glacial Maximum (LGM) in subtropical China might have been the main driver to the species’ allopatric differentiation. Scientific conservation and sustainable utilization for wild C. dielsiana germplasm resources were subsequently proposed.

The propagation and multiple scattering of non-homogeneous shear waves resulting from two cavities embedded in exponential functional graded materials (FGMs) were investigated, and the dynamic stress around the two cavities derived. The non-homogeneous scattering fields of shear waves around the cavities are analytically expressed by using the wave function expansion method. The interaction of non-homogeneous scattering fields between the two cavities is described accurately. The dynamic stresses around the cavities under different geometrical and physical parameters are graphically illustrated and analyzed. Analysis shows that the non-homogeneous properties of FGMs exhibit a significant effect on the dynamic stress around the cavities. The effect of the non-homogeneous properties of FGMs on the dynamic stress is also dependent on the gradation direction, the distance between the two cavities, the relative position of the two cavities and the incident frequency of waves. A comparison with other existing s...

The mechanism of hydrolysis of nitroguanidine has been studied theoretically. The molecular geometries have been fully optimized at AM1 level of theory for reagent, activated and product complexes for hydrolysis of nitroguanidine in neutral, acidic and alkaline media, respectively. In neutral and acidic media, both activated complexes have four-membered ring structures, and the reaction-coordinated eigenvectors show heavy-atom reorganization and proton transfer to be truly concerted in both cases. In alkaline medium, the hydrolysis also involves activated complex. The calculated activation energies for the hydrolysis of nitroguanidine in neutral, acidic and alkaline media are 278.2 kJ/mol, 330.2 kJ/mol and 213.0 kJ/mol, respectively. Der Mechanismus der Hydrolyse von Nitroguanidin wurde rechnerisch untersucht. Die Molekul-Geometrien wurden voll optimiert auf das Niveau der AM1-Theorie fur die reagierenden, aktivierten und Produkt-Komplexe der Hydrolyse des Nitroguanidins in neutralem, saurem und alkalischem Medium. In neutralem und saurem Medium haben die beiden aktivierten Komplexe eine 4-gliedrige Ringstruktur und die mit der Reaktion koordinierten Eigenvektoren zeigen Umordnung der schweren Atome und Protonenubertragung, was in beiden Fallen tatsachlich gleichzeitig verlaufen mus. Auch im alkalischen Medium entstehen bei der Hydrolyse aktivierte Komplexe. Die berechneten Aktivierungsenergien fur die Hydrolyse des Nitroguanidins in neutralem, saurem und alkalischem Medium betragen jeweils 278,2 kJ/mol, bzw. 330,2 kJ/mol, bzw. 213,0 kJ/mol. Le mecanisme d'hydrolyse de la nitroguanidine a ete etudie de facon theorique. Les geometries moleculaires ont ete totalement optimisees au niveau de la theorie AM1 pour les complexes reactants, actives et de produits pour l'hydrolyse de la nitroguanidine en milieu respectivement neutre, acide et alcalin. En milieu neutre et acide, les deux complexes actives ont des structures annulaires a 4 membres, et les vecteurs propres coordonnes a la reaction presentent une reorganisation des atomes lourds et un transfert de protons, ce qui doit effectivement se produire simultanement dans les deux cas. En milieu alcalin, l'hydrolyse englobe egalement un complexe active. Les energies d'activation calculees pour l'hydrolyse de nitroguanidine en milieux neutre, acide et alcalin sont respectivement de 278,2 kJ/mol, et 330 kJ/mol et 213,0 kJ/mol.

The banding and electronic structures of a series of long-chain macromolecules of cellulose, 2-, 3-, 6-mononitrocellulose, 2,3-,2,6-, 3,6-dinitrocellulose and trinitrocellulose as well as their structural units (i.e. single-, double- or three-ring systems) have been calculated by both the EH and CNDO/2 methods. The increase of molecular total energies is consistent with the decrease of their stabilities at the three conformations of gg, gt and tg. The Mulliken bond order of O—NO2 bond is the smallest in each molecule at any of the three conformations, which indicates that this bond is the weakest, and supports the view of initial homolytic cleavage of O—NO2 bond on slow thermal decomposition. The band gap at the edge of the first Brillouin zone far surpasses 5 eV for cellulose, and is less than 3 eV for mono-, di-, and trinitrocellulose. The results show that cellulose is a typical insulator, as we know, and it can be predicted that nitrocellulose has electric conductivity similar to that of semiconductor.