Guided architecture trade space exploration: fusing model-based engineering and design by shopping

Software and Systems Modeling - Advances in model-based system engineering have greatly increased the predictive power of models and the analyses that can be run on them. At the same time, designs...     

The formation of cuprous oxide films on α-brass stress-corrosion fracture surfaces

A study has been made of the nature of the fracture surface of α-brass specimens after failure by stress-corrosion cracking in pH 7·2 Mattsson's solution. The yellow colour of the stress-corrosion fracture surface points to a possible inadequacy in the “tarnish-rupture” model of the mechanism of this instance of stress-corrosion. The techniques of cathodic reduction and chemical dissolution have been used to remove any oxide present on the original fracture surface. On subsequent re-immersion in pH 7·2 Mattsson's solution, the stress-corrosion fracture surface remains untarnished, whereas the mechanical fracture surface rapidly acquires a black tarnish film. Comparison of plateau lengths obtained on further cathodic reduction has shown that for equivalent times of re-immersion, a much thicker film forms on the mechanical fracture region than on the stress-corrosion region of the fracture surface. The experimental results are interpreted as being inconsistent with the “tarnish-rupture” model but consistent with a stress-corrosion mechanism involving dezincification at the crack tip.     

Environmentally-induced cracking of magnesium

Slow strain rate tensile tests have been carried out on commercially pure and high purity magnesium specimens in air and in de-aerated, pH 10, 10^?3 M Na₂SO₄ solution under different environmental conditions. The results of these tests have been supplemented by studies of the failed specimens using optical metallography and scanning electron fractography. It is shown that under certain environmental conditions magnesium is susceptible to hydrogen embrittlement and environmentally-induced cracking in Na₂SO₄ solution. The source of the hydrogen, even under anodic polarization, is the local action cathodic reaction. Atomic hydrogen can only enter, and embrittle, the metal matrix at active, bare, passive-film-free pit walls. Therefore if pitting is promoted by anodic polarization cracking is more severe; conversely if pitting is prevented by cathodic polarization, embrittlement and cracking are not observed. Atomic hydrogen produced by cathodic polarization is prevented by the presence of the Mg(OH)₂ passive film from entering the metal and causing embrittlement; furthermore even at a strain rate of5.7 × 10^?6 s^-1passivation is sufficiently rapid to prevent entry of hydrogen during tensile testing of cathodically polarized specimens. Depending on the grain size and purity the embrittled magnesium specimens exhibit either a completely transgranular quasicleavage fracture surface morphology or a mixed brittle intergranular and quasi-cleavage transgranular fracture surface morphology. Possible mechanisms for the hydrogen-induced cracking are discussed briefly in light of the demonstrated reversibility of hydrogen uptake. It is suggested that hydrogen embrittlement and cracking may account for spalling and disintegration of magnesium anodes and may contribute to the negative different effect.     

Cutting carbon emissions from electricity generation

Oregon’s Clean Electricity and Coal Transition Plan does not prohibit delivery of coal-fired electricity to retail loads. Coal-fired electricity cannot be excluded from retail delivery given the interconnected Western grid. It also mandates new renewable performance standards that are the costliest approach of the policies reviewed. Cost adders tied to carbon emissions from all thermal generation are an effective approach to carbon reduction.     

Florence Duomo project (1420–1436): Learning best project management practice from history

This paper narrates the project management of the construction of the Florence Duomo by Filippo Brunelleschi in the fifteenth century. This was the most significant dome project in Europe in 1300 years, and possibly the most significant, innovative and complex project of the Renaissance era (Colombo and Lanzavecchia, 1997). It still stands as the largest brick dome ever built. In order to achieve what seemed technically impossible at the time, Brunelleschi researched and adapted the construction and project management of the Pantheon in Rome in the second century. The paper allows us in turn to learn both product and process innovation from this case study, both of which are essential to contemporary project management practice. The case is valuable in understanding key drivers of project management success, and illustrates the substantial potential for learning, and therefore knowledge transfer, from previous historical projects and experiences.     

非挥发性记忆体Read Disturb测试方法的研究

DDF是一种高容量的NAND Flash。以DDF产品为例,研究和讨论了它的Read Disturb测试方法。受测试时间的限制,只能选择局部的存储区间进行DDF的Read Disturb测试。这样局部区间的测试结果是否能够代表整个芯片的性能,设计了一套实验,对这个课题进行了研究和讨论。依据非挥发性记忆体产品的特性,主要以阈值电压的分布为参考来评价DDF芯片性能的一致性和性能恶化趋势的一致度。最后的实验结果证明了这种测试方法的正确性和合理性。这种分析方法也可以用于其他非挥发性记忆体产品的其他可靠性测试项目的评估。     

The effect of ion implantation on the corrosion behaviour of pure iron—I. Argonion implantation

High purity iron has been implanted with relatively high (ca. 5 at.%) surface concentrations of argon by means of ion implantation. Using electrometric reduction it has been shown that at some stage during or after the implantation process the natural air-formed film on the iron is thickened, producing an oxide film comparable to a thermally grown film formed at low oxygen partial pressure (～ 30μN m^?2) at 475K. The factor responsible for this enhanced film growth has not been identified. Using a three sweep potentiokinetic polarization technique it has also been shown that once the thickened air formed film is removed by cathodic polarization there are no significant differences between the polarization behaviour of unimplanted and argon implanted iron that cannot be explained by changes in surface roughness associated with the implantation process.It is concluded that earlier reports that the implantation of metals with inert species such as argon confers enhanced corrosion resistance may be attributed to the thickening of the air-formed oxide film and not to the presence of the implant species per se. Furthermore, in the investigation of the effect of implantation of more active implant species it is necessary to take account of the film thickening that occurs during implantation.     

斜坡电流测试应用与比较方法研究

讨论了斜坡电流测试的相关参数如电流斜坡速率、步长及电流倍增速率对测试结果击穿电荷具有的严重影响。指出斜坡电流测试中各个参数的设定、影响及其相关性,使斜坡电流测试的结果具有可比较性。同时,讨论了由于斜坡电流测试本身的特性,击穿电荷具有非连续性,针对击穿电荷的非连续性,提供了一种统计上的数据处理方法,并且根据工程上不同的定性比较结果提供了不同的统计比较方法,可以对非连续的斜坡电流测试结果进行定量的统计比较。在产品验证或生产线出现异常时,能够进行统计上的比较,给出定量的结果。据此能对生产线的稳定性或异常事件对产品的影响给出明确的结论,为受影响的产品的处置提供定量的数据支持。这是首次对斜坡电流测试数据的统计定量分析。