Mechanical responses of anchoring structure under triaxial cyclic loading

Dynamic load on anchoring structures(AS)within deep roadways can result in cumulative damage and failure.This study develops an experimental device designed to test AS under triaxial loads.The device enables the investigation of the mechanical response,failure mode,instability assessment criteria,and anchorage effect of AS subjected to combined cyclic dynamic-static triaxial stress paths.The results show that the peak bearing strength is positively correlated with the anchoring matrix strength,anchorage length,and edgewise compressive strength.The bearing capacity decreases significantly when the anchorage direction is severely inclined.The free face failure modes are typically transverse cracking,concave fracturing,V-shaped slipping and detachment,and spallation detachment.Besides,when the anchoring matrix strength and the anchorage length decrease while the edgewise compressive strength,loading rate,and anchorage inclination angle increase,the failure intensity rises.Instability is determined by a negative tangent modulus of the displacement-strength curve or the continued deformation increase against the general downward trend.Under cyclic loads,the driving force that breaks the rock mass along the normal vector and the rigidity of the AS are the two factors that determine roadway stability.Finally,a control measure for surrounding rock stability is proposed to reduce the internal driving force via a pressure relief method and improve the rigidity of the AS by full-length anchorage and grouting modification.

Estimation of Evapotranspiration from Faber Fir Forest Ecosystem in the Eastern Tibetan Plateau of China Using SHAW Model

Understanding the hydrological processes of forest ecosystems in Tibetan Plateau is crucial for protecting water resources and the environment, especially considering that evapotranspiration is the most dominant hydrologic process in most forest systems. SHAW, as a physically based, hydrological model, provides a useful tool for understanding and analyzing evapotranspiration processes. Using the measured data of a faber fir forest ecosystem in eastern Tibetan Plateau, this paper assessed the model performance in simulating evapotranspiration and variability and transferability of the model parameters. Comparison of the simulated results by SHAW to the measured data showed that SHAW performed satisfactorily. Based on analyzing the simulated results by the calibrated and validated SHAW, some ET characteristics of faber fir forest ecosys-tem in the eastern Tibetan Plateau were found: 1) Daily plant transpiration is low, and daily ET mainly comes from surface evaporation including canopy, litter and soil evaporation. Peak ET rate was approxi-mately 4mm/day, occurring around late July. 2) Solar radiation is the most important factor accounting for daily ET variation, while air temperature is the secondary, wind speed and air relative humidity are minor and soil water storage is the least important among all the related factors. 3) The ratio of annual ET to pre-cipitation for the faber fir forest ecosystem in eastern Tibetan Plateau is low (18%) compared with the other forest ecosystems owing to high-elevation, high atmospheric humidity and low annual temperature.

Spatial and Temporal Variations in Available Soil Nitrogen—A Case Study in Kobresia Alpine Meadow in the Qinghai-Tibetan Plateau, China

Elucidating the factors that determine the effects of temporal and spatial variation of nutrients is important for analyzing the characteristics of an ecosystem. The goal of this paper was to estimate how values obtained using a particular sampling approach correlated with the actual data for an entire plot. The mesh partition method was employed to divide an integrated observing field (IOF) located at the Haibei National Field Research Station of an alpine grassland ecosystem, China, into 25 subplots. Five of the 25 subplots were randomly selected for soil sampling and to determine the source of variations in soil nutrient content from 2001 to 2012. The results showed that, contributions of temporal and spatial variation in available nitrogen in the 0 - 10 cm soil layer accounted for 47.3% and 52.7%, respectively. The contribution of spatial variance was higher than that of temporal variance especially in the surface soil layers. The available soil nitrogen content in the alpine meadow was not obviously affected by fluctuations in rainfall and temperature. Increasing the number of samples could reduce calculation errors in measuring available soil nitrogen content, while collecting a reasonable number of samples can save time and labor.

基于Pro/Engineer的蜗杆程序化设计

本文以便携式小型旋耕机蜗杆减速器的设计方法为基础,使用Pro/ENGINEER的二次开发软件包Pro/TOOLKIT开发了蜗杆的程序化设计系统。该设计系统界面简单、直观,操作方便,降低了设计者的工作量,缩短了蜗杆蜗轮齿廓曲线绘制的设计周期,并易于进行蜗杆传动的运动仿真及蜗杆减速器的运动分析。

Ordered SrTiO_3 Nanoripples Induced by Focused Ion Beam

Ordered nanoripples on the niobium-doped SrTiO_3 surfaces were fabricated through focused ion beam bombardment. The surface morphology of the SrTiO_3 nanoripples was characterized using in situ focused ion beam/scanning electron microscopy. The well-aligned SrTiO_3 nanostructures were obtained under optimized ion irradiation conditions. The characteristic wavelength was measured as about 210 nm for different ion beam currents. The relationship between the ion irradiation time and current and SrTiO_3 surface morphology was analyzed. The presented method will be an effective supplement for fabrication of SrTiO_3 nanostructures that can be used for ferroelectric and electronic applications.

Linking leaf elemental traits to biomass across forest biomes in the Himalayas

Plants require a number of essential elements in different proportions for ensuring their growth and development.The elemental concentrations in leaves reflect the functions and adaptations of plants under specific environmental conditions.However,less is known about how the spectrum of leaf elements associated with resource acquisition,photosynthesis and growth regulates forest biomass along broad elevational gradients.We examined the influence of leaf element distribution and diversity on forest biomass by analyzing ten elements(C,N,P,K,Ca,Mg,Zn,Fe,Cu,and Mn)in tree communities situated every 100 meters along an extensive elevation gradient,ranging from the tropical forest(80 meters above sea level)to the alpine treeline(4200 meters above sea level)in the Kangchenjunga Landscape in eastern Nepal Himalayas.We calculated communityweighted averages(reflecting dominant traits governing biomass,i.e.,mass-ratio effect)and functional divergence(reflecting increased trait variety,i.e.,complementarity effect)for leaf elements in a total of 1,859 trees representing 116 species.An increasing mass-ratio effect and decreasing complementarity in leaf elements enhance forest biomass accumulation.A combination of elements together with elevation explains biomass(52.2%of the variance)better than individual elemental trait diversity(0.05%to 21%of the variance).Elevation modulates trait diversity among plant species in biomass accumulation.Complementarity promotes biomass at lower elevations,but reduces biomass at higher elevations,demonstrating an interaction between elevation and complementarity.The interaction between elevation and mass-ratio effect produces heterogeneous effects on biomass along the elevation gradient.Our research indicates that biomass accumulation can be disproportionately affected by elevation due to interactions among trait diversities across vegetation zones.While higher trait variation enhances the adaptation of species to environmental changes,it reduces biomass accumulation,especially at higher elevations.

青藏高原植被结构变化反映环境变迁

草地植被结构对于其生产和生态功能至关重要,但大尺度信息严重匮乏.本研究结合多源遥感数据和深度学习,在区域尺度上厘清了青藏高原高寒草地基于群系的植物群落结构空间格局,并比较了其历史变化.过去40年,高寒草甸在高寒草地中的比例从50%上升到69%,反映了变暖变湿的环境变化.此外,高寒草甸和高寒草原中高山嵩草草甸和紫花针茅草原的优势度分别增强到76%和92%.其中,气候因子驱动了紫花针茅草原近些年的分布;高山嵩草草甸近些年的分布则并非完全由气候驱动,人类活动可能起重要作用.本研究首次探索了区域尺度植被结构特征与历史变化,为认识青藏高原草地变化的驱动力及其空间异质性提供了新视角.

高寒小嵩草草甸可能成为青藏高原相同地理和气候单元下多种类型草地的偏途演替状态

高寒嵩草(Kobresia)草甸是青藏高原冬春放牧草场的主体,在放牧强度分异的条件下可以形成特征迥异的稳态。然而,目前还不清楚在不同放牧强度下其他类型草地是否可以演替成为这些稳态。本研究通过土壤剖面特征推断其历史植物群落特征,以植物群落现场调查确定其现实植物群落特征,以非结构式问卷调查确定草地放牧强度,采用多元回归树模型分析导致草地稳态转化的节点。研究结果表明,高寒灌丛草甸和旱化沼泽草甸在过度放牧条件下均可转化成为高寒矮嵩草(K.humilis)草甸和高寒小嵩草(K.pygmaea)草甸,从而使高寒灌丛草甸和旱化沼泽化草甸进入高寒矮嵩草草甸退化演替序列,最终转化成为黑土滩-杂类草次生裸地。以放牧强度为分节点,最多可以将这些植物群落划分为4类稳态,各稳态转化的节点依次为11.0、8.0、5.5羊/ha。所有研究草地总体表现为随放牧强度的增高地上总生物量呈下降趋势。其中,11.0羊/ha是草地转化成为黑土滩杂类草次生裸地的节点。放牧强度改变可以影响植物群落特征及其演替方向,进而改变草地的畜牧生产服务能力,因此放牧强度可以作为反映牧场畜牧生产服务能力的表观指标。未来牧场的可持续发展策略应以草畜平衡为主,合理控制放牧强度,增加草地生产附加值和延伸畜牧业产业链以实现区域草场生态和生产效益的双赢。

Self-stabilizing maintenance process in plant communities of alpine meadows under different grazing intensities

Backgrounds:Grazing prohibition and reduced grazing intensity,as two important“vegetation close-to-nature recovery”methods,have been suggested as economical and effective technologies for enhancing forage production.However,numerous studies have found that the yield of forage could be increased by removing or reducing grazing in a short time in some steady stage of alpine Kobresia meadows,but not in others.To reveal the mechanism behind this phenomenon,we proposed a series of experiments.Methods:We monitored the plant and soil characteristics in the key steady stages of Kobresia meadows under reduced and prohibited grazing conditions in the same geographic and climatic environments in the northeastern Qinghai-Tibet Plateau for 6 years.We estimated the relationships between the plant community and soil nutrients and obtained the following results.Results:All measured variables were positively correlated with each other.The plant community structure had higher path coefficients to aboveground biomass,soil organic matter,total nitrogen,and nitrate nitrogen than to other factors.The plant community structure played an important role in response to grazing intensity.Different plant functional groups(PFGs)had different responses to grazing intensity,which led to plant community re-establishment or re-organization under different grazing intensities.Poaceae and Kobresia were more sensitive to grazing intensity than other PFGs,and the ratio of Kobresia biomass(including Kobresia humilis and Kobresia pygmaea)to the total biomass of Poaceae and Kobresia could be used as an indicator of regime shifts within plant communities.With Kobresia pygmaea as the dominant species,the prohibition of grazing was not an efficient approach to increase the yield in the steady stages because this treatment needed more time to recover aboveground biomass.If Poaceae is the dominant PFG,grazing should only be prohibited for 3 years in the steady stages because the aboveground biomass will decrease if grazing is prohibited for more than 3 years.Conclusions:Therefore,the different steady stages of alpine meadows require different recovery methods to increase recovery efficiency and speed.

Synergies between microsites of plant communities and steady-stage alpine meadows on the Qinghai-Tibetan Plateau

Background:Due to the effects of climate change and overgrazing in recent decades,alternative stable states in the alpine Kobresia meadow degradation process have coexisted in the same geographical and climatic environment,with variations occurring among microsites.Methods:We used a space-for-time substitution approach to explore the synergies of microsite variation according to its numerical characteristics and the proportion of each stable state at various stages of succession in alpine Kobresia meadows on the Qinghai-Tibetan Plateau.Results:(1)The highest average aboveground biomass in summer was 196.2±20.3 gm^(-2),with significantly higher levels of biomass in≤3.65 sheep unit ha^(-1) than in other levels of grazing intensity,while the parameters showed no significant differences among grazing intensity levels in>3.65 sheep unit ha^(-1).(2)The importance of plant functional groups,aboveground biomass,and niche breadth of Poaceae and Cyperaceae significantly decreased as the grazing intensity increased.(3)The effects of≥0°C accumulated temperature,total precipitation,altitude,longitude,and latitude cumulatively contributed less than 20%of the variation in the distribution of functional group characteristics across microsites.Conclusions:(1)Overgrazing decreases primary production in alpine Kobresia meadows,but ecosystem responses regulate plant community structure and botanical components so as to partially counteract grazing disturbance.(2)Overgrazing changed the proportion of microsites,which in turn led to regime shift in the plant community and subsequent synergies between the microsites of plant communities and their stable states.

New approaches for evaluation of soil health, sensitivity and resistance to degradation

Assessment of soil health requires complexevaluation of properties and functions responsible for abroad range of ecosystem services. Numerous soil qualityindices (SQI) have been suggested for the evaluation ofspecific groups of soil functions, but comparison of variousSQI is impossible because they are based on a combinationof specific soil properties. To avoid this problem, wesuggest an SQI-area approach based on the comparison ofthe areas on a radar diagram of a combination of chemical,biological and physical properties. The new approach isindependent of the SQI principle and allows rapid andsimple comparison of parameter groups and soils. Anotherapproach analyzing the resistance and sensitivity ofproperties to degradation is suggested for a detailedevaluation of soil health. The resistance and sensitivityof soil properties are determined through comparison withthe decrease of soil organic carbon (SOC) as a universalparameter responsible for many functions. The SQI-areaand resistance/sensitivity approaches were tested based on quences after the ab and on ment of agricultural soils. Both the SQI-area and the resistance/sensitivity approaches areuseful for basic and applied research, and for decisionmakersto evaluate land-use practices and measure thedegree of soil degradation.

Managed grassland alters soil N dynamics and N2O emissions in temperate steppe

Reclamation of degraded grasslands as managed grasslands has been increasingly accelerated in recent years in China. Land use change affects soil nitrogen（N） dynamics and nitrous oxide（N2O） emissions. However, it remains unclear how large-scale grassland reclamation will impact the grassland ecosystem as a whole. Here, we investigated the effects of the conversion from native to managed grasslands on soil N dynamics and N2O emissions by field experiments in Hulunber in northern China. Soil（0-10 cm）, nitrate（NO3-）,ammonium（NH4＋）, and microbial N were measured in plots in a temperate steppe（Leymus chinensis grassland） and two managed grasslands（Medicago sativa and Bromus inermis grasslands） in 2011 and 2012. The results showed conversion of L. chinensis grassland to M.sativa or B. inermis grasslands decreased concentrations of NO3--N, but did not change NH4-N . Soil microbial N was slightly decreased by the conversion of L. chinensis grassland to M.sativa, but increased by the conversion to B. inermis. The conversion of L. chinensis grassland to M. sativa（i.e., a legume grass） increased N2O emissions by 26.2%, while the conversion to the B. inermis（i.e., a non-legume grass） reduced N2O emissions by 33.1%. The conversion from native to managed grasslands caused large created variations in soil NO3-＋-N and NH4-N concentrations. Net N mineralization rates did not change significantly in growing season or vegetation type, but to net nitrification rate. These results provide evidence on how reclamation may impact the grassland ecosystem in terms of N dynamics and N2O emissions.

High-voltage 4H-SiC PiN diodes with the etched implant junction termination extension

This paper presents the design and fabrication of an etched implant junction termination extension（JTE）for high-voltage 4H-SiC PiN diodes. Unlike the conventional JTE structure, the proposed structure utilizes multiple etching steps to achieve the optimum JTE concentration range. The simulation results show that the etched implant JTE method can improve the blocking voltage of SiC PiN diodes and also provides broad process latitude for parameter variations, such as implantation dose and activation annealing condition. The fabricated SiC PiN diodes with the etched implant JTE exhibit a highest blocking voltage of 4.5 kV and the forward on-state voltage of 4.6 V at room temperature. These results are of interest for understanding the etched implant method in the fabrication of high-voltage power devices.