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Presented herein is an investigation into the stretching and fracture behavior of single-walled carbon nanotubes (SWCNT) subjected to axial tensile load at various temperatures. This study is carried out using molecular dynamics (MD) simulation at temperatures ranging from 200 K to 2200 K. The authors find that single-walled carbon nanotubes exhibit obvious temperature and chirality dependent properties. The values of tensile strain and tensile strength of zigzag (12, 0) and armchair (7, 7) SWCNTs with similar radii decrease with increase in temperature, but decline slightly on different slopes. The stress-strain curves of zigzag and armchair SWCNTs vary significantly when the temperature is more than 1200 K. Our studies suggest temperature and chirality play an important role in determining the tensile strength and tensile strain of SWCNT.

A visible light transmittance machine vision detection method was put forward to measure the bonding quality of micro devices made by transparent materials with specific compositions and structures.The performance requirements of main components in the system hardware was analyzed,and the image processing techniques for the detection system were researched.The visible light transmittance machine vision detection system captured the image with the main components of the light source,camera,lens and the computer and implemented quality testing by image subtraction,gray histogram adjustment,image filtering and image binarization.Experimental results indicate that the proposed detection method can detect the bonding gaps of the micro devices made by transparent materials sensitively and effectively,and the detection accuracy of flaw size is about 10 μm.The results meet the detection requirements of micro devices for bonding quality and verify that the method is efficient,non-contact,non-destructive and non-polluting.

Fire disturbance is one of the key processes affecting forest succession in boreal forest ecosystems.Variations in disturbance characteristics have an important effect on ecosystem properties and processes.Due to the diversity of topography,fuel heterogeneity and micro-climatic conditions during a fire,the intensity of fires is quite variable,producing landscapes in different mosaic patterns.Although the resulting heterogeneity of fire characteristics(e.g.,burn severity) has been widely recognized as an important driver of boreal forest regeneration,its effects on early post-fire tree recruitment has not been thoroughly studied in boreal forests of the Great Xing′an Mountains.Early post-fire tree recruitment can reflect future forest structures and succession pathways.A clear understanding of the controls and mechanisms of post-fire tree recruitment is therefore necessary for us to predict future forest dynamics,devise reasonable forest management practices,and properly maintain natural landscape structures. In addition to fire characteristics,environmental conditions and pre-fire vegetation can also have important effects on post-fire tree recruitment.Environmental conditions such as elevation,slope,aspect,soil can affect post-fire seed germination.Pre-fire vegetation can affect seed banks and the distribution of post-fire seed sources.Post-fire tree recruitment in boreal forest ecosystems,as a whole,is influenced by multiple factors,including elevation,slope,aspect,soil depth,pre-fire forest type,pre-fire stand age,burn severity,and burned patch size.The objective of this study is to discover which factors are the most important controls on post-fire conifer and broadleaf tree recruitment and to predict what succession pathways will take place. We selected Huzhong and Xinlin Forestry Bureaus as study area to carry out field survey.The forest type of the study area is typical in Great Xing′an Mountains with major tree species being white birch(Betula platyghylla) and Dahuirian larch(Larix gmelini).Post-fire forest succession in this study area can be divided into two pathways,which are self-replacement(i.e.,the composition of immediately re-established post-fire tree species is the same as pre-fire canopy dominated ones,and continues as canopy dominant) and relay succession(i.e.,different tree species successively assume post-fire canopy dominance,which is firstly dominated with early-successional tree species and gradually by late successional ones).This study analyzed relative influences of various controls(environmental conditions,pre-fire vegetation,and fire disturbance characteristics) on post-fire tree recruitment and their marginal effects using a boosted regression tree method and data collected from 55 recently burned sites.Our results showed that 1) elevation was the most important factor for conifer tree recruitment;2) slope was the most important factor for broadleaf tree recruitment;3) time-since-last-fire was the most important control of the post-fire conifer seedling proportion,and forest type was the second;4) Post-fire conifer seedling proportion was higher in plots with conifer forest as pre-fire forest type than that with mixed or broadleaf forest;5) conifer tree regeneration after intermediate-severity fires was better than that after low-and high-severity fires.Our study suggested that self-replacement often occurred in the sites with single-species forest as the pre-fire forest type;while relay succession often occurred in the sites with mixed forest.