Mg2Si单轴应变的结构和电子性能

基于密度泛函理论的第一性原理计算方法研究了Mg2 Si半导体沿[001]方向单轴应变下的结构、力学性质以及电子性质.计算结果表明：无应变时晶格参数和弹性常数与其他理论及实验值吻合的很好.施加应变后,其与应变方向垂直的晶格常数随应变值呈近似线性变化.通过应力-应变曲线和Born力学稳定性判据,确定了Mg2Si化合物在拉伸、压缩过程中的稳定范围和理想强度.Mg2Si的电子布居和电子态密度分析,表明Si-Mg之间的显示离子键特性,并给出了在拉伸压缩过程中Mg和Si原子轨道电子对总的态密度影响.     

非常光线在单轴晶体中的折射定律

非常光线在各向异性媒质中传播不遵从折射定律 ,亦无确定的折射率 .从寻常光线和非常光线在单轴晶体中传播具有 2种不同子波面的假定出发 ,应用惠更斯原理 ,推导出非常光线在单轴晶体中传播的折射定律和折射率的表达式 .     

基于离散单元法农田土壤单轴压缩模型的建立及参数校核

建立基于离散单元法的农田土壤单轴压缩可靠模型,并较准确模拟真实土壤力学性能,在有限元理论的基础上,借助Flunet-UDF能将模型网格信息写出的特点,利用EDEM软件自定义工厂生成不饱和土壤单轴压缩模型,并对其进行仿真试验。仿真试验结果表明:切向接触刚度和曲线的上升段与应变轴夹角、峰值、下降段与应变轴夹角均有关,上升段、下降段与应变轴夹角、峰值随切向接触刚度增大而增大;曲线的峰值在随临界切向应力减小而减小,下降段落点随临界切向应力减小而离原点越近;下降段与应变轴夹角随法向接触刚度增大而增大;下降段与应变轴夹角随临界法向应力减小而增大。当法向接触刚度为210 MN/m3、切向接触刚度为80 MN/m3、临界法向应力为30kPa和临界切向应力为8kPa时,该组黏结参数能较可靠表征含水率为10.5%的耕地土壤力学特性。     

Microcracking and Chloride Penetration of Concrete under Uniaxial Compression

A non-destructive method of evaluation of specific crack area was used to characterise microcracking in concrete prisms during uniaxial compression loading and unloading. Chloride profiles were also measured after the same concretes were exposed to chloride environment. The relation among microcracking, stress-strength ratio and chloride penetration of concrete were analysed based on the experimental results. Under compressive load, the apparent chloride diffusion coefficient decreases until about one third of the ultimate load. Further increase of compressive load improves the chloride diffusion coefficient again. There is a close link between microcracking and stress-strength ratio. The index of specific crack area can be used to indicate the microcracking and study chloride transport behaviour into concrete under the influence of microcracking.     

单轴压缩条件下岩石破损过程的CT试验分析

采用工业计算机层析(ICT)设备与全数字液压实验系统EHF-EG200KN试验机,对大台煤矿冲击倾向性煤层底板岩石试样进行了单轴压缩荷载作用下的CT试验,得到了单轴压缩荷载作用下不同应力阶段岩石试样微裂纹发展的CT图像。通过对CT图像灰度值的分析,得到单轴压缩荷载作用下岩石的损伤破裂过程。为进一步研究煤层底板岩石的破坏及冲击地压的发生机理提供依据。     

Functional evaluation of the various calculation methods for precompression stress

Precompression stress (σ_p) is commonly used as an indicator for the load carrying capacity of a soil and its stress history. Several calculation methods have been proposed to determine σ_p, but they have proven to be not interchangeable. The aim of this study was to perform a functional evaluation of seven existing methods to test which method would be most recommended to assess soil strength in cultivated fields. This was achieved by investigating the relation of the obtained σ_p of undisturbed soil samples to other soil properties and stress history. Additionally, the robustness of the methods was evaluated by checking their sensitivity to perturbation of the measured strains. The two most commonly used methods, the Casagrande method and Gompertz model fit method, were found to be the least suitable to calculate σ_p. These methods lack robustness and do not yield a significant relation with the relevant soil properties or stress history. Better results were obtained with Intersecting linear regressions or at the inflection point of a fourth-degree polynomial.     

单旋翼电动无人机对莲雾及荔枝树喷雾效果的试验

为了初步探究单旋翼电动无人机对莲雾与荔枝果树航空喷施的雾滴沉积效果,论证航空作业方式的可行性。针对2种果树设计了包含4个独立作业架次的喷施验证试验,研究了HB-Y-15L与DN-18N单旋翼电动无人机以常规作业参数对莲雾与荔枝果树进行往复式喷施作业时,对应果树冠层各层正反面采样区域的雾滴沉积分布情况。结果表明：在0.3～1.5 m/s的微风条件下,当2种型号的单旋翼电动无人机分别以距果树冠层顶部1 m的飞行高度、2 m/s的飞行速度对莲雾与荔枝果树进行往复式航空喷施作业时,机型对于莲雾、荔枝果树垂直各层采样区域的雾滴沉积水平的影响并不是很显著;经对比分析,HB-Y-15L型无人机喷施雾滴在莲雾树树冠各层间的雾滴穿透性（18.69%）较佳,DN-18N型无人机喷施雾滴在荔枝树树冠各层间的雾滴穿透性（21.25%）较佳;但2种机型在莲雾、荔枝果树各层正反面采样区域测得的雾滴分布均匀性值普遍处于50%以上水平,最高值高达210.06%,均表现出了较差的雾滴分布均匀性,果树沉积均匀性方面研究亟需加强;同时,在未来进行莲雾、荔枝果树航空喷施作业时,为了保证最佳的喷施有效沉积量,建议无人机配套使用喷雾角为80°的小喷雾角度的喷头。该研究结果初步揭示了单旋翼电动无人机应用在莲雾与荔枝果树上的喷施效果,可为合理喷施农药、提升农药利用率提供参考,对进一步推动莲雾、荔枝果树飞防作业普及具有重要的指导意义。     

不同应力状态下裂隙岩体水力劈裂试验研究

以水泥砂浆作为类岩石材料,采用水-固-热耦合试验系统、电液伺服万能试验机、动态数据采集分析系统以及自主设计研制的高压水密封装置分别进行了不同注入流量条件以及单轴压应力作用下裂隙岩体水力劈裂试验。研究结果表明:无轴向拉压作用下,注入流量越大,试样劈裂破坏历时越短,越容易发生劈裂破坏,且试样水力劈裂起裂水压与劈裂水压的比值Pini/PIc与注入流量呈线性关系;注入流量不变的情况下,垂直裂缝走向的轴向压应力对试样水力劈裂起抑制作用,平行裂缝走向的轴向压应力较小时(0.1~0.3 MPa)对砂浆试样水力劈裂起抑制作用,较大时(0.4~0.5 MPa)对砂浆试样水力劈裂起促进作用。     

苹果幼树三级单轴延伸整形修剪技术研究

为简化苹果树整形修剪技术,提高早期产量和果实品质,对苹果幼树三级（即中心干、主枝和结果枝组）单轴延伸整形修剪技术试验园与小冠疏层形果园的树体生长、结果和用工成本等指标进行了分析与比较。结果表明：苹果幼树三级单轴延伸整形修剪技术试验园的树高、干高、主枝数和主枝梢角角度均显著提高;单位面积枝量、长中短枝数量、中短枝比例以及小枝组数量均显著增加;产量和单果重显著增加,着色面积、可溶性固形物含量和硬度等指标有一定程度的提高;总用工量和用工成本均有所降低。因此,在苹果幼树上应用三级单轴延伸整形修剪技术,具有促进苹果早期丰产、提高果实品质以及降低用工投入的效果。