In forest ecosystems, gap formation changes the allocation of abiotic resources and thus affects the survival and growth of understory plants. However, how tree seedling survival and growth respond to low-temperature ...In forest ecosystems, gap formation changes the allocation of abiotic resources and thus affects the survival and growth of understory plants. However, how tree seedling survival and growth respond to low-temperature events and the influencing mechanisms remain unclear. To clarify how low-temperature event limits the survival and growth of tree seedlings in the montane regions of eastern Liaoning Province, northeast China, we investigated temperature and light intensity within secondary forest gaps, and the survival and growth of Juglans mandshurica seedlings after a low-temperature event in the spring of 2014. Damage to seedlings due to low temperature sig- nificantly varied in different aspects. Seedlings in gaps on southeast-facing slopes were the most seriously damaged, followed by those in gaps on northeast-facing slopes. In contrast, seedlings in west-facing gaps and in control plots without slope aspect were not damaged. The freezing injury index for seedlings was negatively correlated with minimum temperature （r = - 0.608, P 〈 0.01）, but it was positively correlated with light intensity （r= 0.818, P 〈 0.01）. In addition, height and root collar diameter of damaged seedlings were significantly lower than those of the undamaged seedlings （P 〈 0.01） during the early growing season （April-July）, but no significant difference were observed during the late growing season （July-Oc- tober） （P 〉 0.05）. The extent of seedling damage was directly related to slope aspect. Low temperature and high light intensity were found to be the dominant factors affecting extent of damage to seedlings on southeast- and northeast-facing slopes.展开更多
Band structures of one-dimensional （1D） photonic crystals （PCs） containing dispersive left-handed metamaterials are studied theoretically. The results show that the structure possesses a type of photonic band gap ...Band structures of one-dimensional （1D） photonic crystals （PCs） containing dispersive left-handed metamaterials are studied theoretically. The results show that the structure possesses a type of photonic band gap originating from total internal reflection （TIR）. In contrast to photonic band gaps corresponding to zero average refractive index and zero phase, the TIR gap exhibits sharp angular effect and has no polarization effect. It should also be noted that band structures of transverse electric （TE） and transverse magnetic （TM） mode waves are exactly the same in the PCs we studied.展开更多
The electronic and optical properties, including band structure, density of states （DOS）, absorption rate, refractive index, and dielectric function, of anatase TiO2 codoped with N and first transition elements are ...The electronic and optical properties, including band structure, density of states （DOS）, absorption rate, refractive index, and dielectric function, of anatase TiO2 codoped with N and first transition elements are investigated using the plane wave pseudopotential method based on the density functional theory. The calculation results show that TiO2 codoping with N and first transition elements （Sc, V, Cr, Mn, and Fe） lead to significant reduction of conduction band relative to the Fermi level, reduction of band gap width, formation of new donor, and acceptor impurity levels below the conduction band and above the valence band, and cause some redshifts of optical absorption band edge with the amount of redshift decrease in the following order： N-Fe 〉 N-Cr 〉 N-Mn. Further, the synergistic effect of shallow donor and acceptor levels enhances light excitation for effective separation of electron-hole pairs and enhancement of light absorption ability, thereby increasing the TiO~ photocatalytic properties. This study reveals that the visible-light absorption ability of the codoped anatase TiO2 decreases in the order of N Fe 〉 N Cr 〉 N-Mn 〉 N-Sc 〉 N-V 〉 N, and does not monotonically follow the dopant atomic number. Especially, in N-Cr codoped TiO2, the 4s atomic orbit of Cr is not completely filled, which hybridized with the p electronic orbit most probably acts as photo-generated electron trap centers resulting in higher photocatalytie activity than that of N-Mn codoped TiO2.展开更多
基金supported by the National Key Research and Development Program of China(2016YFC0500302)the National Nature Scientific Foundation Project of China(31200432)
文摘In forest ecosystems, gap formation changes the allocation of abiotic resources and thus affects the survival and growth of understory plants. However, how tree seedling survival and growth respond to low-temperature events and the influencing mechanisms remain unclear. To clarify how low-temperature event limits the survival and growth of tree seedlings in the montane regions of eastern Liaoning Province, northeast China, we investigated temperature and light intensity within secondary forest gaps, and the survival and growth of Juglans mandshurica seedlings after a low-temperature event in the spring of 2014. Damage to seedlings due to low temperature sig- nificantly varied in different aspects. Seedlings in gaps on southeast-facing slopes were the most seriously damaged, followed by those in gaps on northeast-facing slopes. In contrast, seedlings in west-facing gaps and in control plots without slope aspect were not damaged. The freezing injury index for seedlings was negatively correlated with minimum temperature （r = - 0.608, P 〈 0.01）, but it was positively correlated with light intensity （r= 0.818, P 〈 0.01）. In addition, height and root collar diameter of damaged seedlings were significantly lower than those of the undamaged seedlings （P 〈 0.01） during the early growing season （April-July）, but no significant difference were observed during the late growing season （July-Oc- tober） （P 〉 0.05）. The extent of seedling damage was directly related to slope aspect. Low temperature and high light intensity were found to be the dominant factors affecting extent of damage to seedlings on southeast- and northeast-facing slopes.
基金the Shanghai Rising-Star Program(No.05QMX1459)the National Natural Science Foundation of China(No.60508018)
文摘Band structures of one-dimensional （1D） photonic crystals （PCs） containing dispersive left-handed metamaterials are studied theoretically. The results show that the structure possesses a type of photonic band gap originating from total internal reflection （TIR）. In contrast to photonic band gaps corresponding to zero average refractive index and zero phase, the TIR gap exhibits sharp angular effect and has no polarization effect. It should also be noted that band structures of transverse electric （TE） and transverse magnetic （TM） mode waves are exactly the same in the PCs we studied.
基金supported by the National Natural Science Foundation of China(Nos.61274128 and 61106129)the Natural Science Foundation of Chongqing(No.CSTC2013JCYJA0731)
文摘The electronic and optical properties, including band structure, density of states （DOS）, absorption rate, refractive index, and dielectric function, of anatase TiO2 codoped with N and first transition elements are investigated using the plane wave pseudopotential method based on the density functional theory. The calculation results show that TiO2 codoping with N and first transition elements （Sc, V, Cr, Mn, and Fe） lead to significant reduction of conduction band relative to the Fermi level, reduction of band gap width, formation of new donor, and acceptor impurity levels below the conduction band and above the valence band, and cause some redshifts of optical absorption band edge with the amount of redshift decrease in the following order： N-Fe 〉 N-Cr 〉 N-Mn. Further, the synergistic effect of shallow donor and acceptor levels enhances light excitation for effective separation of electron-hole pairs and enhancement of light absorption ability, thereby increasing the TiO~ photocatalytic properties. This study reveals that the visible-light absorption ability of the codoped anatase TiO2 decreases in the order of N Fe 〉 N Cr 〉 N-Mn 〉 N-Sc 〉 N-V 〉 N, and does not monotonically follow the dopant atomic number. Especially, in N-Cr codoped TiO2, the 4s atomic orbit of Cr is not completely filled, which hybridized with the p electronic orbit most probably acts as photo-generated electron trap centers resulting in higher photocatalytie activity than that of N-Mn codoped TiO2.
