Most Hydraulically Efficient Riprap-Lined Drainage Channels

Dimensions of the most hydraulically efficient trapezoidal and triangular drainage channels (that is, those with the smallest possible cross-section areas) whose banks are lined with loose rock riprap are found along with the stable stone diameter by solving a constrained nonlinear minimization problem. The problem statement is made dimensionless and less complicated by normalizing solution variables and combining parameters into two dimensionless quantities that describe the composite roughness of a channel and the stability of the rock lining. Normalized values of section bottom width, water depth, and rock diameter, along with the channel side-slope ratio, are found numerically. Results of the analysis are presented graphically and, when practical, in the form of empirical expressions. The solutions, which are comprehensive, give cross-section dimensions and the rock size needed to maintain a stable bank lining, greatly simplify design of hydraulically efficient riprap-lined open channels.     

High quality relaxed Ge layers grown directly on a Si(0 0 1) substrate

After a long period of developing integrated circuit technology through simple scaling of silicon devices, the semiconductor industry is now embracing technology boosters such as strain for higher mobility channel material. Germanium is the logical supplement to enhance existing technologies, as its material behaviour is very close to silicon, and to create new functional devices that cannot be fabricated from silicon alone (Hartmann et al. (2004) [1]). Germanium wafers are, however, both expensive and less durable than their silicon counterparts. Hence it is highly desirable to create a relaxed high quality Ge layer on a Si substrate, with the provision that this does not unduly compromise the planarity of the system. The two temperature method, proposed by Colace et al. (1997) [2], can give smooth (RMS surface roughness below 1 nm) and low threading dislocation density (TDD <10⁸ cm⁻²) Ge layers directly on a Si(0 0 1) wafer (Halbwax et al. (2005) [3]), but these are currently of the order of 1-2 μm thick (Hartmann et al. (2009) [4]).We present an in depth study of two temperature Ge layers, grown by reduced pressure chemical vapour deposition (RP-CVD), in an effort to reduce the thickness. We report the effect of changing the thickness, of both the low temperature (LT) and the high temperature (HT) layers, emphasising the variation of TDD, surface morphology and relaxation.Within this study, the LT Ge layer is deposited directly on a Si(0 0 1) substrate at a low temperature of 400 °C. This low temperature is known to generate monolayer islands (Park et al. (2006) [5]), but is sufficiently high to maintain crystallinity whilst keeping the epitaxial surface as smooth as possible by suppressing further island growth and proceeding in a Frank-van der Merwe growth mode. This LT growth also generates a vast number of dislocations, of the order of 10⁸-10⁹ cm⁻², that enable the next HT step to relax the maximum amount of strain possible. The effect of varying the HT layer thickness is studied by depositing on a LT layer of fixed thickness (100 nm) at a higher growth temperature of 670 °C. We find that the HT layer allows Ge-on-Ge adatom transport to minimise the surface energy and smooth the layer. The final step to the technique is annealing at a high temperature that allows the dislocations generated to glide, increasing the degree of relaxation, and annihilate. We find that annealing can reduce the TDD to the order of 10⁷ cm⁻², but at a cost of a significantly roughened surface.     

超光滑光学基底表面原子力显微镜测试方法

原子力显微镜(AFM)是评价亚纳米级表面粗糙度σRMS最主要的测试仪器,但其测试结果会因采样条件(采样间距、采样点数)及测量点位置变化而改变。以AFM测试超光滑光学基底随机表面为例,应用累积功率谱理论建立了确定合理采样条件的方法,避免了采样条件选取不当带来的数据丢失或冗余;通过全局优化选取测量点和局部优化选取测量点相结合,降低了样品表面区域性差异给测试结果带来的不确定性,并大大减少了获得可靠测试结果所需的测试量。上述工作为超光滑光学基底AFM测试提供了有效方案。     

The sputter cross section of a surface-vacancy island

Using molecular-dynamics simulation we investigate the effect of surface-vacancy islands on ion-induced sputtering. As an exemplary case, the sputtering of a Pt(1 1 1) surface by 5 keV Ar⁺ ions incident at 83° towards the surface normal is investigated. We find that only the ascending step of the island induces sputtering. Wide vacancy islands exhibit the direct-hit, indirect-hit and channeling zones previously identified for surface steps and adatom islands. A special role is played by the descending step edge. Even though it is not sputtered itself, it deflects ion trajectories and may direct them to the ascending step edge thus enhancing sputtering. We derive a simple criterion based on the shadow cone of the descending step to decide whether a vacancy island contributes to sputtering or not.     

Ni伴随WC颗粒复合沉积层的表面粗糙度和显微结构

The intermediate layer was prepared by nickel doped with WC particles electroplating.The parameters,including current density and temperature,were studied.The measured methods,which consisted of surface roughometer and SEM,were used to character the roughness and micrograph.Based on the results,it was shown that the optimized parameters of the composite were as follows,temperature 65 ℃,current density 5 A/dm2 and pH 6.5.In the range of optimized parameters,the roughness Ra was from 4.5 to 6.7 μm.From the SEM micrograph,the particles on the surface were well distributed.The nickel content,which affected the binding force,was determined by the electroplating time.     

重型车车身涂装桔皮缺陷案例解析

随着汽车工业的发展,完美的涂装外表已不仅仅局限于轿车行业,很多重型车制造商为了满足顾客的更高要求、提升竞争力,对其表面质量越来越重视。通过对驾驶室涂装中出现严重桔皮的故障排除,浅析了桔皮的成因机理及测定方法,并根据在现场生产中对车身板材、涂装用漆、喷涂环境及操作工技术等产生桔皮因素的监测和整改,为在生产中控制桔皮缺陷提供了必要依据。     

电力设备三维网格模型自适应鲁棒水印算法

提出一种新的电力设备三维网格模型鲁棒水印算法,介绍了该算法在电力多媒体信息安全中的应用。该算法首先对电力设备三维网格模型进行离散曲率估计,找出模型中脐点;结合网格模型离散法向量和局部粗糙度,通过自适应主方向投影实现水印嵌入。实验结果表明,该水印算法能有效抵抗加性噪声、仿射变换、网格简化、网格剪切等多种网格变换和攻击,具有较强的不可感知性和鲁棒性。     

钛片电化学抛光工艺及耐蚀性研究

以含氯离子的乙二醇溶液为抛光液,研究了槽压、温度、时间对钛片表面电化学抛光效果的影响,得到电化学抛光的最佳工艺为:槽压30V,温度50℃,时间180 s.采用扫描电镜、Tafel极化曲线及表面粗糙度测试等方法,研究了电化学抛光后钛片的表面形貌、耐蚀性、粗糙度等性能,同时与传统的机械抛光及化学抛光方法进行了比较.结果表明...     

超声振动铣削2A12表面粗糙度实验研究

利用小径立铣刀对铝合金进行超声振动铣削实验,重点探讨了超声振幅与每齿进给量对工件槽底表面粗糙度的影响.实验结果表明:槽底表面粗糙随着超声振幅的增大而增大,在每齿进给量fZ<4μm/z时槽超声振幅为主要影响因素;每齿进给量fZ>6μm/z时每齿进给量为主要影响因素.在超声振动铣削加工中应尽量选择小进给量可获得较小槽底表面粗糙度.通过扫面电镜对工件微观形貌观测证实了施加振动后脉冲切削和断续切削双重作用导致槽底表面粗糙度增大.     

粗糙表面的统计研究

论述了粗糙表面的表征方法,根据表面形成的随机特性,将粗糙表面的高度分布归为二项式分布.根据粗糙度取值的不同,讨论了泊松分布表面和高斯分布表面的高度分布特点和表面截面积及相对密度的分布情况.对表面接触状态进行了初步分析,认为表面接触存在一定的嵌入深度,并且根据嵌入深度可以估算表面接触面积.分析结果表明:泊松表面和高斯表面...