长白山北坡植物群落复杂性的海拔梯度变化(英文)

应用梯度格局法在长白山北坡海拔700m-2600m的坡面上每100 m海拔设置一样地,共计20块样地,通过对同一群落各样方间的相异性测定,对各海拔植物群落的复杂性进行了分析。结果表明,以主林层乔木种的二元数据计算的结果,除亚高山岳桦林外,其它各海拔群落的样方间均表现出较高的相异性,特别是低海拔的阔叶红松林平均相异系数达0.74,明显高于其它植被类型;暗针叶林各群落间差异不大,相对而言1400 m群落样方间的相异性略高于其它群落,表现出过渡性群落树种组成的复杂性;岳桦林树种组成简单,样[(\267\275\274\344\322\262\261\355\317\326\263\366\275\317\270\337\265\304\\317\340\313\306\320\324\241\243)-0.1(\322\324\271\340\304\276\326\326\265\304\266\376\324\252\312\375\276\335\\274\306\313\343\265\304\310\272)]落内的相异性,虽低海拔的阔叶红松林总体上高于其它群落,但差异趋势并不像乔木种那么明显。以各草本植物与所有植物种的二元数据计算的各海拔群落内样方间的相异性,表现出非常相近的趋势,群落内样方间草本植物及所有植物种均以阔叶红松林及高山冻原差异最大,暗针叶林基本稳定于比较相近的水平。图3表1参8。

Size Effect and Geometrical Effect of Polycrystals and Thin Film/Substrate System in Micro-indentation Test

Micro-indentation test at scales on the order of sub-micron has shown that the measured hardness increases strongly with decreasing indent depth or indent size, which is frequently referred to as the size effect. Simultaneously, at micron or sub-micron scale, the material microstructure size also has an important influence on the measured hardness. This kind of effect, such as the crystal grain size effect, thin film thickness effect, etc., is called the geometrical effect by here. In the present research, in order to investigate the size effect and the geometrical effect, the micro-indentation experiments are carried out respectively for single crystal copper and aluminum, for polycrystal aluminum, as well as for a thin film/substrate system, Ti/Si3N4. The size effect and geometrical effect are displayed experimentally. Moreover, using strain gradient plasticity theory, the size effect and the geometrical effect are simulated. Through comparing experimental results with simulation results, length-scale parameter appearing in the strain gradient theory for different cases is predicted. Furthermore, the size effect and the geometrical effect are interpreted using the geometrically necessary dislocation concept and the discrete dislocation theory. Member Price: $0; Non-Member Price: $25.00

Md Simulation Of Dislocation Mobility During Cutting With Diamond Tip On Silicon

By means of Tersoff and Morse potentials, a three-dimensional molecular dynamics simulation is performed to study atomic force microscopy cutting on silicon monocrystal surface. The interatomic forces between the workpiece and the pin tool and the atoms of workpiece themselves are simulated. Two partial edge dislocations are introduced into workpiece Si, it is found that the motion of dislocations does not occur during the atomic force microscopy cutting processing. Simulation results show that the shear stress acting on dislocations is far below the yield strength of Si. (c) 2008 Elsevier Ltd. All rights reserved.

Microstructure Study Of Laser Welding Cast Nickel-Based Superalloy K418

Experiments of laser welding cast nickel-based superalloy K418 were conducted. Microstructure of the welded seam was characterized by optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy dispersive spectrometer (EDS). Mechanical properties of the welded seam were evaluated by microhardness. The corresponding mechanisms were discussed in detail. Results show that the laser welded seam have non-equilibrium solidified microstructures consisting of Cr-Ni-Fe-C austenite solid solution dendrites as the dominant and some fine and dispersed Ni-3(Al,Ti) gamma' phase as well as little amount of MC needle carbides and particles enriched in Nb, Ti and Mo distributed in the interdendritic regions, cracks originated from the liquation of the low melting points eutectics in the HAZ grain boundary are observed, the average microhardness of the welded seam and HAZ is higher than that of the base metal due to alloy elements' redistribution of the strengthening phase gamma'. (C) 2008 Elsevier B.V. All rights reserved.

Micromechanics analysis on evolution of crack in viscoelastic materials

A preliminary analysis on crack evolution in viscoelastic materials was presented. Based on the equivalent inclusion concept of micro-mechanics theory, the explicit expressions of crack opening displacement delta and energy release rate G were derived, indicating that both delta and G are increasing with time. The equivalent modulus of the viscoelastic solid comprising cracks was evaluated. It is proved that the decrease of the modulus comes from two mechanisms: one is the viscoelasticity of the material; the other is the crack opening which is getting larger with time.

铝粉快速反应光谱中AlOB~2Σ~＋→X~2Σ~＋发射光谱的研究

在由光学多道分析仪收集的氢氧气体爆轰激励下铝粉快速反应光谱中，观察到ＡｌＯＢ２Σ＋→Ｘ２Σ＋跃迁Δｖ＝０带系的光谱特征与通常铝氧化反应的光谱特征不同。经分析是因为存在一个从４６７ｎｍ开始向长波方增强的连续辐射，它改变了该波长区ＡｌＯ分子的辐射特征。这一连续辐射可能是由铝与水蒸汽发生水合反应生成，而处于不同激发态的多原子分子ＨＡｌＯＨ产生

剪切带状分叉的力学条件

在已论证过的应变软化效应对形成剪切带状分叉的作用的基础上,本文研究了:(1)什么受力情况最易激发剪切带(2)采用什么力学模型和参数可以模拟材料中的曲线型带状分叉。

瓦斯煤尘爆炸火焰温度的测定

用自己研制的红外高温辐射计,在一端开口的直径200cm、长2900cm的大型地面模拟爆炸试验管道上,在不同的条件下(瓦斯-空气,瓦斯-空气-煤尘),对瓦斯煤尘爆炸火焰的光谱特性进行了测量。根据测量的波长λ=4.346μm的绝对辐射强度和我们选择的物理模型,获得了不同状态下瓦斯煤尘爆炸火焰的温度。

测量土、岩石介质中的动态应力用的压电式应力计

本文介绍一种压电式应力计,它的主要性能是:测量量程为10-1000kgf/cm~2;响应时间小于7μs;线性误差小于士1％;综合应力测量误差小于±10％,该应力计可用于测量土、岩石和混凝土介质中的动态应力,也可用于测量动态力和流体介质中的动态压力。

方形管道中湍流水流某些特征的激光多普勒法测量及其与圆形管道的对比

用激光多普勒测速法测量了雷诺数从4.76×10~3到4.76×10~4的矩形管道中的湍流水流。其结果与相同雷诺数时的圆形管道的流动就某些流动特征进行了对比。引人注目的是,在矩形管道内速度分布更“平坦”,且随雷诺数的增加而强烈地趋向更加均匀,湍流强度也比圆管流动的大得多。在横截面的中线上,对四种不同雷诺数所得的速度分布数据与普适的湍流速度外部定律有较好的符合。为了保持湍流的功率谱以及减小频带加宽,在测量仪器方面使用了某些技术。由Berman和Dunning所给出的有关速度梯度加宽的效应的式子也从本测量中得到了实验数据的支持。