分享阳光--比尔的公寓楼

这幢位于瑞士比尔郊区的公寓高三层,由8套大小不同的住宅单元所构成,所处位置能够俯瞰整个小镇,具有极佳的视野。下面的部分是跃层式的二层公寓,上面一层则是普通公寓。楼顶为公共活动区域,设有孩子们的游戏室,其屋顶形式与相邻的建筑风格颇为近似。基地东南向的陡坡非常理想地     

Driving Mechanisms of Delamination Related Reliability Problems in Exposed Pad Packages

Exposed pad packages were introduced in the late 1980s and early 1990s because of their excellent thermal and electrical performance. Despite these advantages, the exposed pad packages experience a lot of thermo-hygro-mechanical related reliability problems during qualification and testing. Examples are die lift, which occurs predominantly after moisture sensitivity level conditions, and die-attach to leadframe delamination leading to downbond stitch breaks during temperature cycling. In this chapter, nonlinear finite element (FE) models using fracture mechanics based J-integral calculations are used to assess the reliability problems of the exposed pad package family. Using the parametric FE models any geometrical and material effects can be explored to their impact on the occurrence diepad delamination, and dielift. For instance the impact of diepad size is found to be of much less importance as the impact of die thickness is. Using the fracture mechanics approach, the starting location for the delamination from thermo-hygro-mechanical point of view is deducted. The results indicate that when diepad delamination is present, cracks are likely to grow beneath the die and dielift will occur. The interaction between dielift and other failure modes, such as lifted ball bonds, are not found to be very significant. The FE models are combined with simulation-based optimization methods to deduct design guidelines for optimal reliability of the exposed pad family.     

Numerical study on PEMFC’s geometrical parameters under different humidifying conditions

Steady-state and three-dimensional simulations were carried out to study the influences of geometrical parameters on the performance of PEMFC under different hydrating conditions. Flow fields, species transport, transport of water in polymer membrane and movement of liquid water in cathode and anode porous layers were determined, in order to accomplish a complete estimation of ohmic and concentration losses of PEMFC power. The geometrical parameters were thickness of the polymer membrane, cathode catalyst layer as well as gas channel to rib width ratio. Every simulation was made under different relative humidities of inlet flows (50 and 100%) for every change of characteristic length. Results show that the influence of the geometrical parameters on ohmic and concentration losses is of considerable importance. The performance of PEMFC is seriously affected under dehydrating conditions. However, such performance may be considerably improved by using suitable geometrical parameters. Cathode and anode liquid saturation may not only affect the transport of species, but also the polymer electrolyte water content. These results show the importance of simultaneously calculating both the water absorption and desorption through the polymer electrolyte and the liquid saturation in the cathode and anode porous mediums to obtain an actual view of ohmic and concentration losses of the PEMFC performance.     

Subnanometer-scale chemistry and structure of α-iron/molybdenum nitride heterophase interfaces

The local chemistry and structure of α-iron/molybdenum nitride heterophase interfaces is studied on a subnanometer scale by atom-probe field-ion microscopy (APFIM), three-dimensional atom-probe microscopy (3DAPM) and both conventional transmission electron microscopy (CTEM) and highresolution electron microscopy (HREM). Molybdenum nitride precipitates are generated by annealing Fe-2 at. pct Mo-X, where X=0.4 at. pct Sb or 0.5 at. pct Sn, at 550 °C or 600 °C, in an ammonia/hydrogen mixture. Internal nitridation at 550 °C produces thin, coherent platelet-shaped molybdenum nitride precipitates. Nitridation at 600 °C generates a much coarser structure with semicoherent thick plate-shaped and spheroidal precipitates in addition to the thin-platelet structure. The APFIM and 3DAPM analyses of the heterophase interfaces show substantial segregation of the solute species Sn and Sb only at the coarse precipitates, with Gibbsian interfacial excesses of up to 7±3 nm⁻², whereas the broad faces of the thin platelets have no detectable segregation. The TEM and HREM analyses show that the coarse precipitates are semicoherent, whereas the thin platelets are either coherent or have much fewer misfit dislocations than geometrically necessary. This demonstrates that Sn and Sb segregation is related to the presence of misfit dislocations at the interfaces of the coarse precipitates. This article is based on a presentation made at the symposium entitled “The Mechanisms of the Massive Transformation,” a part of the Fall 2000 TMS Meeting held October 16–19, 2000, in St. Louis, Missouri, under the auspices of the ASM Phase Transformations Committee.