一种基于PDCA的软件过程控制与改进模型

CMM/CMMI(capabilitymaturitymodel/CMMintegration)自1999年开始为中国软件企业所接受并逐步得以推广,但目前中国实施CMM/CMMI的企业还不多,有些企业实施效果并不理想.通过调查软件企业在实施CMM/CMMI过程中存在的问题,并对发现的问题及其负面影响进行分析,提出了基于PDCA(plan-do-check-action)的软件过程控制与改进模型,开发了SoftPM软件质量管理平台.该平台的广泛应用表明,该模型对提高CMM/CMMI的企业软件过程的效率和改善实施效果很有帮助.

基于CMMI-ACQ的信息技术和服务安全采购模型

进入21世纪,软件外包及采购已逐渐成为信息技术服务使用组织的首要选择,软件的安全性直接影响着软件的使用,组织财产及人员生命安全。因而对采购组织而言,采购安全性直接关系到组织的各方面利益。目前的相关研究均未能将安全属性纳入采购过程考虑,忽略了采购过程本身的安全性。本文提出了一种基于CMMI-ACQ的安全采购模型,在CMMI-ACQ模型的基础上,引入了ISO27000安全标准的要求。本文旨在关注采购过程中的安全性目标和实践,为组织提供实际的安全采购指导,帮助组织进行安全的信息技术和服务采购,保证软件及其应用的安全性,避免组织因安全隐患带来的损失。

一种改进的类比估算方法及案例研究

软件成本估算是软件工程领域的重要活动之一。类比估算由于具有易于理解、不受数据规模的影响、不需要本地校准、降低异常点对估算精度的影响等优势，所以是软件成本估算常用的方法之一。项目属性集的选择、相似度函数定义和修正求解是类比估算三个比较重要的方面。 通过对比分析目前类比估算相似度的定义，得出其存在的问题是：没有充分利用模型和历史项目集信息从而在一定的数据集上可能降低估算精度。针对这种问题，本文提出一种改进的类比估算方法，该方法充分利用了模型和历史项目集的相关信息，定义模型属性信息空间上由第一类曲线积分计算的弧长为相似度。 项目属性集选择相关程度比较低的因子以解决由于因子之间相关程度高对估算精度产生影响的问题；修正求解采用基于相似度倒数或平方倒数加权法以解决相似项目数难以确定的问题。 在成本驱动因子的定义和管理、成本估算模型的支持与集成、模型校准、模型精度分析这四个方面，本文分析了现行的成本估算软件存在的问题及发展趋势。根据分析结果，并结合改进的类比估算方法开发了改进的类比估算工具ImpAnalogy。该工具基于Eclipse RCP框架，采用MVC架构实现了数据管理、因子管理、模型精度分析、模型共享等模块。 本文使用工具ImpAnalogy进行了三个案例研究。 案例一：为一个没有使用任何估算方法和估算工具的企业提供一个估算精度相对较高的方法和工具。结果表明改进后的类比方法的估算精度高于基于欧氏距离和AMH的类比估算方法、基于模型的指数加权调整方法、COCOMO类型方法和回归方法。 案例二：为一个准备申请CMMI 4级的企业提供一个估算精度较高的方法。结果表明改进后类比方法的估算精度高于采用欧氏距离和AMH的类比估算方法、COQUALMO类型方法，但是低于回归方法。 案例三：采用NASA93数据集验证方法的有效性，增强说服力。结果表明改进后的类比方法的估算精度高于采用欧氏距离的类比估算方法和回归方法；采用基于相似度倒数或平方倒数加权调整算法的估算精度高于单项目调整算法和回归方法。

Dislocation nucleation governed softening and maximum strength in nano-twinned metals

In conventional metals, there is plenty of space for dislocations-line defects whose motion results in permanent material deformation-to multiply, so that the metal strengths are controlled by dislocation interactions with grain boundaries(1,2) and other obstacles(3,4). For nano-structured materials, in contrast, dislocation multiplication is severely confined by the nanometre-scale geometries so that continued plasticity can be expected to be source-controlled. Nano-grained polycrystalline materials were found to be strong but brittle(5-9), because both nucleation and motion of dislocations are effectively suppressed by the nanoscale crystallites. Here we report a dislocation-nucleation-controlled mechanism in nano-twinned metals(10,11) in which there are plenty of dislocation nucleation sites but dislocation motion is not confined. We show that dislocation nucleation governs the strength of such materials, resulting in their softening below a critical twin thickness. Large-scale molecular dynamics simulations and a kinetic theory of dislocation nucleation in nano-twinned metals show that there exists a transition in deformation mechanism, occurring at a critical twin-boundary spacing for which strength is maximized. At this point, the classical Hall-Petch type of strengthening due to dislocation pile-up and cutting through twin planes switches to a dislocation-nucleation-controlled softening mechanism with twin-boundary migration resulting from nucleation and motion of partial dislocations parallel to the twin planes. Most previous studies(12,13) did not consider a sufficient range of twin thickness and therefore missed this strength-softening regime. The simulations indicate that the critical twin-boundary spacing for the onset of softening in nano-twinned copper and the maximum strength depend on the grain size: the smaller the grain size, the smaller the critical twin-boundary spacing, and the higher the maximum strength of the material.

Fracture of colloidal single-crystal films fabricated by controlled vertical drying deposition

Controlled vertical drying deposition method was used to make high-quality single crystal close-packed colloidal films formed of different radii polystyrene latex spheres on glass substrates coming from a low concentration water suspension (0.1% volume fraction). Regardless of the spheres radii the film thickness was about 6.3 microns. However, cracks destroyed the crystalline film structure during the colloidal film growth. The effect of particle radius (85-215 nm range) on film cracking was systematically studied using in situ optical fracture monitoring. Primary parallel cracks run along the vertical growth direction, later followed by secondary branched cracks in-between the primary cracks due to residual water evaporation. Quantitative theoretical relationship between the cracks spacing and particles radius was derived and shows good agreement with experimental observations. Normalized cracks spacing is related to a reciprocal ratio of the dimensionless particle radius.