A generalized nonlinear three-dimensional failure criterion based on fracture mechanics

Based on fracture mechanics theory and wing crack model,a three-dimensional strength criterion for hard rock was developed in detail in this paper.Although the basic expression is derived from initiation and propagation of a single crack,it can be extended to microcrack cluster so as to reflect the macroscopic failure characteristic.Besides,it can be derived as HoekeBrown criterion when the intermediate principal stress σ_(2) is equal to the minimum principal stress σ_(3)(Zuo et al.,2015).In addition,the opening direction of the microcrack cluster decreases with the increase of the intermediate principal stress coefficient,which could be described by an empirical function and verified by 10 kinds of hard rocks.Rock strength is influenced by the coupled effect of stress level and the opening direction of the microcrack clusters related to the stress level.As the effects of these two factors on the strength are opposite,the intermediate principal stress effect is induced.

Experimental investigation on fracturing process of marble under biaxial compression

In this study,servo-controlled biaxial compression tests were conducted on marble specimens to investigate their failure characteristics and fracturing process.The complete stressestrain curves were obtained,and the three-dimensional(3D)features of the failure surfaces were acquired by 3D laser scanning.Acoustic emission(AE)monitoring and moment tensor(MT)analysis were used in combination to better understand the fracturing mechanism of marble under biaxial compression.It was noted that a type of 3D stepwise cracking behaviour occurred on the fracturing surfaces of the examined specimens.The stress dropped multiple times,and a repeated fracturing mode corresponding to the repeated stress drops in the post-peak regime was observed.Three substages,i.e.stress stabilisation,stress decrease and stress increase,were identified for a single fracturing mode.Then quantitative and statistical analyses of the fracturing process at each substage were discussed.Based on the testing results,it was found that at the stress stabilisation substage,the proportion of mixed-mode fractures increased.At the stress decrease substage,the proportion of mixed-mode fractures decreased,and the tensile or shear fractures increased.At the stress increase substage,the proportion of mixed-mode or tensile fractures decreased,and the shear fractures increased.Finally,a conceptual model for the stepwise crack formation was proposed.

Passivated ZnSe nanocrystals prepared by hydrothermal methods and their optical properties

Homogeneous Zn Se nanocrystals were prepared via surfactant-assisted hydrothermal method.Surfactants agent CTAB was used to control the particle morphology and the growth rate.The structure,morphology and optical properties of Zn Se nanocrystals have been investigated by XRD,TEM and luminescence spectroscopy.The results indicated that the size of Zn Se nanocrystals ranged from 3.0 nm to 5.0 nm with cubic zinc blende structure.Zn Se nanocrystals coated by CTAB were revealed high dispersibility and distribution under TEM.Compared to the bulk Zn Se,the absorption edges and photoluminescence peaks of Zn Se nanocrystals were blue shifted to higher energies due to the quantum confinement effect.The emission intensity was strengthened after coated CTAB compared to bare sample.This was mainly due to the surface passivation.Meanwhile,we simply explored the formation mechanism of Zn Se nanocrystal in hydrothermal system.

Screening of Semi-solid Culture Conditions of Armillaria mellea A9

[Objectives]This study was conducted to optimize the germplasm resources of Gastrodia elata and improve the condition of declining G.elata production.[Methods]A scientific and reasonable method was used to screen the optimum nutritional conditions(carbon sources,nitrogen sources,microelements,vitamins)and environmental conditions(pH,temperature,light)of Armillaria mellea A9 growth,so as to screen the medium suitable for the growth of A.mellea.[Results]Under the semi-solid culture condition,the suitable pH range of A.mellea mycelia was 4.0-9.0;the temperature was about 25℃;and the light condition was dark culture.Under the experimental conditions,the optimal carbon source was 25 g/L ethanol;the optimal nitrogen source was 2.5 g/L soy peptone;and the optimum microelement and vitamin were 0.5 g/L MnSO 4,0.5 g/L MgSO 4 and 20 mg/L vitamin B6,respectively.After screening,the growth rate of A.mellea rhizomorph was as high as 13.52 mm/d,and the dry weight of mycelium also reached 0.296 7 g.[Conclusions]This study not only omitted a lot of tedious experiments,but also obtained reliable and scientific experimental results,and achieved the purpose of rejuvenating A.mellea,which is conducive to the further development and utilization of G.elata and its symbiotic fungi.

Spatial network structure of transportation carbon emission efficiency in China and its influencing factors

Grasping the spatial correlation structure of transportation carbon emission efficiency(TCEE)and its influencing factors is significant for promoting high-quality and coordinated development of the transportation industry and the relevant region.Based on the ideal point cross-efficiency(IPCE)model,the social network analysis method was employed herein to explore the spatial correlation network structure of China’s provincial TCEE and its influencing factors.The results obtained showed the following outcomes.(1)During the study period,China’s provincial TCEE formed a complex and multithreaded network association relationship,but its network association structure was still relatively loose and presented the hierarchical gradient characteristics of dense in the east and sparse in the west.(2)The correlation of China’s TCEE formed a block segmentation based on the regional boundaries,and its factional structure was relatively obvious.The eastern region was closely connected with the central region,and generally connected with the western and northeastern regions.The central region was mainly connected with the eastern and western regions,and relatively less connected with the northeastern region.Besides,the northeastern region was weakly connected with the western region.(3)Shanghai,Beijing,Zhejiang,Guangdong,Jiangsu,Tianjin,and other developed provinces were in the core leading position in the TCEE network,which significantly impacted the spatial correlation of TCEE.However,Heilongjiang,Jilin,Xinjiang,Qinghai,and other remote provinces in the northeast and northwest were at the absolute edge of the network,which weakly impacted the spatial correlation of TCEE.(4)Provincial distance,economic development-level difference,transportation intensity difference,and transportation structure difference had significant negative impacts on the spatial correlation network of China’s provincial TCEE.In contrast,the energy-saving technology level difference had a significant positive impact on it.The regression coefficients of transportation energy structure and environmental regulation differences were positive but insignificant;their response mechanism and effects need to be improved and enhanced.

Robust Inference for Time-Varying Coefficient Models with Longitudinal Data

Time-varying coefficient models are useful in longitudinal data analysis. Various efforts have been invested for the estimation of the coefficient functions, based on the least squares principle. Related work includes smoothing spline and kernel methods among others, but these methods suffer from the shortcoming of non-robustness. In this paper, we introduce a local M-estimation method for estimating the coefficient functions and develop a robustified generalized likelihood ratio (GLR) statistic to test if some of the coefficient functions are constants or of certain parametric forms. The robustified GLR test is robust against outliers and the error distribution. This provides a useful robust inference tool for the models with longitudinal data. The bandwidth selection issue is also addressed to facilitate the implementation in practice. Simulations show that the proposed testing method is more powerful in some situations than its counterpart based on the least squares principle. A real example is also given for illustration.

通过应变工程提高有机半导体的迁移率

有机半导体(OSCs)是推动柔性电子发展的关键.然而,其应用一直受到其较低迁移率的阻碍.虽然分子工程和器件工程可以提高OSC迁移率,但近年来进展几乎停滞不前.本研究揭示了有机半导体在应变下的层数依赖电荷输运特性,并通过应变工程可大幅提高其迁移率.施加应变可以减小分子间π-π间距并减少电子-声子散射,从而提高电荷输运效率.我们观察到应变因子和材料厚度之间存在直接相关性,较薄的晶体具有较高的应变因子.使用分子级薄的二维分子晶体,我们观察到迁移率显著提高了58%.我们的研究结果为提高有机半导体的迁移率开辟了新的途径.

青藏高原土地利用与覆被变化的时空特征

青藏高原土地利用与土地覆被变化(LUCC)研究是区域土地科学与全球变化科学研究的重要内容,也是保障高原生态安全屏障功能稳定与提升的科学基础.本文通过对已有LUCC数据与成果的再分析,研究了高原整体LUCC时空特征、典型区LUCC的时空过程及典型类型的变化过程与机制.结果表明:青藏高原土地利用与土地覆被结构稳定,一级地类变化面积比例低于7%,并以单次变化为主,土地覆被状况总体改善.近年来高寒草地覆被状况整体好转、局部退化,林地恢复良好,耕地基本稳定,建设用地显著扩张,裸地轻微减少.人口较为密集的河湟谷地与'一江两河'地区,建设用地、耕地、人工林地等增加明显;藏北高原和三江源等牧区,超载过牧和生态建设的作用均有体现;珠穆朗玛峰国家级自然保护地区土地覆被类型多样、变化复杂,并表现出对气候变化和人类活动有较强的敏感性.高原土地变化研究中还存在现有数据产品数量不足、精度不高,土地利用变化过程及其环境效应认识不够深入等问题,需要加强野外监测和遥感技术的结合,关注LULC在不同时空尺度下的变化特征,同时注重土地利用与土地覆被类型转化和类内渐变,使高原LUCC研究更好地服务于高原生态安全屏障建设和区域可持续发展.

Polyethylene glycol derived carbon quantum dots nanofluids:An excellent lubricant for diamond-like carbon film/bearing steel contact

Polyethylene glycol derived carbon quantum dots nanofluids were synthesized via a slow thermal oxidation process.The size of carbon quantum dots was ca.2 nm and had a decreasing trend with the increase of oxidation time.When used as lubricant in a diamond-like carbon film/bearing steel interface,the nanofluids achieved an ultra-low friction coefficient(μ≈0.02),much lower than that of original polyethylene glycol(μ=0.12).The worn surface analyses revealed that the nanofluids could effectively inhibit the tribo-oxidation of steel counterpart that occurred under original polyethylene glycol lubrication,and hence reduced the abrasion component of friction.Especially,the poly-hydroxyl carbon dots and oxidized polyethylene glycol species in nanofluids induced a hydroxyl-rich sliding interface via their tribochemical reactions with friction surfaces,which promoted the adsorption of polyethylene glycol molecules on sliding surfaces.Along with the mild corrosion wear of steel counterface,this shifted the boundary lubrication to a mixed/film lubrication regime,thereby achieving an ultra-low friction coefficient.The above results suggest that the polyethylene glycol derived carbon quantum dots nanofluids should be a quite excellent candidate lubricant for solid–liquid synergy lubrication based on diamond-like carbon films.