In order to explore the exact nature of deformation defects previously observed in nanostructured Al-Mg alloys subjected to severe plastic deformation, a more thorough examination of the radiation effect on the format...In order to explore the exact nature of deformation defects previously observed in nanostructured Al-Mg alloys subjected to severe plastic deformation, a more thorough examination of the radiation effect on the formation of the planar defects in the high pressure torsion （HPT） alloys was conducted using high-resolution transmission electron microscopy （HRTEM）. The results show that high density defects in the HRTEM images disappear completely when these images are exposed under the electron beam for some duration of time. At the same time, lattice defects are never observed within no-defect areas even when the beam-exposure increases to the degree that holes appear in the areas. Therefore, it is confirmed that the planar defects observed in the HPT alloys mainly result from the significant plastic deformation and are not due to the radiation effect during HRTEM observation.展开更多
We investigated the effects of grazing on natural regeneration, quantity, and diversity of woody species and dominant herb species in Kheyroud forest in northern Iran. We sampled vegetation in 5m2 plots in custom unit...We investigated the effects of grazing on natural regeneration, quantity, and diversity of woody species and dominant herb species in Kheyroud forest in northern Iran. We sampled vegetation in 5m2 plots in custom units, which are demarcated resource areas traditionally used by local livestock producers. The authors quantified number of species, height of seedlings, and diameter of seedlings. Height classes were 0-30 cm, 30-130 cm, and 〉130 cm, and diameter classes were 0-2.5 cm, 2.5-5 cm and 5-7.5 cm. The density of seedlings declined with distance from corral until reaching the custom unit boundary. Most seedlings had diameters of 0-2.5 cm and heights of 0-30 cm. Predominant species, Carpinus betulus and Acer capadocicum, were in plots near the centers of custom units, Fagus orientalis, Acer velutinum, Quercus castanifolia species were dominant in plots near the custom unit boundary. Plant species such as Oplismenus undulatifolius, Euphorbia amygdaloides, Rubusfrutieos and Pteridium aquilinum were dominant in plots nearer to forest corral. Healthy seedlings were more numerous in plots nearest the corral, while defective and deformed seedlings were more abundant away from the corral. We conclude that grazing had negative effects on the quantity and quality of vegetative regeneration. Continuation of overgrazing will not only endanger the sustainability of forest ecosystems, but also will increase the challenge of sustainable forest management.展开更多
As the era of nanoelectronics is dawning,CNT（carbon nanotube）,a one-dimensional nano material with outstanding properties and performances,has aroused wide attention.In order to study its optical and electrical prop...As the era of nanoelectronics is dawning,CNT（carbon nanotube）,a one-dimensional nano material with outstanding properties and performances,has aroused wide attention.In order to study its optical and electrical properties,this paper has researched the influence of tension-twisting deformation,defects,and mixed type on the electronic structure and optical properties of the armchair carbon nanotube superlattices doped cyclic alternately with B and N by using the first-principle method.Our findings show that if tension-twisting deformation is conducted,then the geometric structure,bond length,binding energy,band gap and optical properties of B,N doped carbon nanotube superlattices with defects and mixed type will be influenced.As the degree of exerted tension-twisting deformation increases,B,N doped carbon nanotube superlattices become less stable,and B,N doped carbon nanotube superlattices with defects are more stable than that with exerted tension-twisting deformations.Proper tension-twisting deformation can adjust the energy gap of the system;defects can only reduce the energy gap,enhancing the system metallicity;while the mixed type of 5%tension,twisting angle of 15° and atomic defects will significantly increase the energy gap of the system.From the perspective of optical properties,doped carbon nanotubes may transform the system from metallicity into semi-conductivity.展开更多
基金Project (50971087) supported by the National Natural Science Foundation of ChinaProject (BK2012715) supported by the Basic Research Program (Natural Science Foundation) of Jiangsu Province, China+1 种基金Project (10371800) supported by the Research Council of Norway under the NEW Light (NEWLIGHT) Metals of the Strategic Area (SA) MaterialsProject (11JDG070) supported by the Senior Talent Research Foundation of Jiangsu University, China
文摘In order to explore the exact nature of deformation defects previously observed in nanostructured Al-Mg alloys subjected to severe plastic deformation, a more thorough examination of the radiation effect on the formation of the planar defects in the high pressure torsion （HPT） alloys was conducted using high-resolution transmission electron microscopy （HRTEM）. The results show that high density defects in the HRTEM images disappear completely when these images are exposed under the electron beam for some duration of time. At the same time, lattice defects are never observed within no-defect areas even when the beam-exposure increases to the degree that holes appear in the areas. Therefore, it is confirmed that the planar defects observed in the HPT alloys mainly result from the significant plastic deformation and are not due to the radiation effect during HRTEM observation.
文摘We investigated the effects of grazing on natural regeneration, quantity, and diversity of woody species and dominant herb species in Kheyroud forest in northern Iran. We sampled vegetation in 5m2 plots in custom units, which are demarcated resource areas traditionally used by local livestock producers. The authors quantified number of species, height of seedlings, and diameter of seedlings. Height classes were 0-30 cm, 30-130 cm, and 〉130 cm, and diameter classes were 0-2.5 cm, 2.5-5 cm and 5-7.5 cm. The density of seedlings declined with distance from corral until reaching the custom unit boundary. Most seedlings had diameters of 0-2.5 cm and heights of 0-30 cm. Predominant species, Carpinus betulus and Acer capadocicum, were in plots near the centers of custom units, Fagus orientalis, Acer velutinum, Quercus castanifolia species were dominant in plots near the custom unit boundary. Plant species such as Oplismenus undulatifolius, Euphorbia amygdaloides, Rubusfrutieos and Pteridium aquilinum were dominant in plots nearer to forest corral. Healthy seedlings were more numerous in plots nearest the corral, while defective and deformed seedlings were more abundant away from the corral. We conclude that grazing had negative effects on the quantity and quality of vegetative regeneration. Continuation of overgrazing will not only endanger the sustainability of forest ecosystems, but also will increase the challenge of sustainable forest management.
基金supported by the National Natural Science Foundation of China(No.51371049)the Natural Science Foundation of Liaoning Province(No.20102173)
文摘As the era of nanoelectronics is dawning,CNT（carbon nanotube）,a one-dimensional nano material with outstanding properties and performances,has aroused wide attention.In order to study its optical and electrical properties,this paper has researched the influence of tension-twisting deformation,defects,and mixed type on the electronic structure and optical properties of the armchair carbon nanotube superlattices doped cyclic alternately with B and N by using the first-principle method.Our findings show that if tension-twisting deformation is conducted,then the geometric structure,bond length,binding energy,band gap and optical properties of B,N doped carbon nanotube superlattices with defects and mixed type will be influenced.As the degree of exerted tension-twisting deformation increases,B,N doped carbon nanotube superlattices become less stable,and B,N doped carbon nanotube superlattices with defects are more stable than that with exerted tension-twisting deformations.Proper tension-twisting deformation can adjust the energy gap of the system;defects can only reduce the energy gap,enhancing the system metallicity;while the mixed type of 5%tension,twisting angle of 15° and atomic defects will significantly increase the energy gap of the system.From the perspective of optical properties,doped carbon nanotubes may transform the system from metallicity into semi-conductivity.
