Thermal oxidation for crystalline silicon solar cells exceeding 19% efficiency applying industrially feasible process technology

Thermal oxides are commonly used for the surface passivation of high‐efficiency silicon solar cells from mono‐ and multicrystalline silicon and have led to the highest conversion efficiencies reported so far. In order to improve the cost‐effectiveness of the oxidation process, a wet oxidation in steam ambience is applied and experimentally compared to a standard dry oxidation. The processes yield identical physical properties of the oxide. The front contact is created using a screen‐printing process of a hotmelt silver paste in combination with light‐induced silver plating. The contact formation on the front requires a short high‐temperature firing process, therefore the thermal stability of the rear surface passivation is very important. The surface recombination velocity of the fired oxide is experimentally determined to be below S ≤ 38 cm/s after annealing with a thin layer of evaporated aluminium on top. Monocrystalline solar cells are produced and 19·3% efficiency is obtained as best value on 4 cm² cell area. Simulations show the potential of the developed process to approach 20% efficiency. Copyright © 2008 John Wiley & Sons, Ltd.     

DRAG REDUCTION IN ARTIFICIALLY ROUGHENED PIPES

The influence of an extremely rough surface on the drag reducing properties of polymer solutions is studied by pressure drop measurements in a rough pipe. It is shown that the onset of drag reduction for a homogeneous dilute polymer solution in a rough pipe occurs at the same wall shear stress as in a smooth pipe of the same diameter. In addition, the maximum drag reduction is almost the same in both types of pipes. Similar results are found for so-called heterogeneous drag reduction obtained by injecting a concentrated polymer solution in the centre of the pipe. The injected polymer solution, which is convected along the centre of the pipe as an elastic thread, disintegrates into fine polymer threads in the rough pipe leading to an increased drag reduction. In this case the injection of the same amount of polymer in the form of a concentrated solution is more effective than a homogeneous polymer solution.     

现代楼梯的空间造型

对于现代室内建筑来说,楼梯已是一种既具有功能,又可使居室生辉的产品.以建筑师与业主的要求为基础,造型与设计多姿多彩.螺旋楼梯是为了节约空间而设计的.过去的楼梯一般单独位于入口的前厅,占地面积大、造价高.现在的楼梯早已被融为居室的一部分,据楼梯制造者说,这也是木质楼梯长久不衰的原因所在.     

Interactive faceted search and exploration of open social media data on a touchscreen mobile phone

A central challenge of semantic ambient media applications is designing smart user interfaces that are able to dynamically deal with an a-priori unknown number of data categories and data instances received live from different Linked Open Data sources while at the same time being intuitive and easy to use. In the mobile world, this challenge is even more difficult as the mobile devices have limited interaction possibilities and smaller display size. In this paper, we tackle this challenge and present the user-centered, iterative design of a mobile application for faceted search and exploration of a large, multi-dimensional data set of open social media on a touchscreen mobile phone. The application is called Mobile Facets and provides live retrieval and interactive search and exploration of resources like places, persons, organizations, and events originating from different, integrated social media sources like DBpedia, Eventful, Upcoming, Flickr, and GeoNames. In contrast to existing work, we do not know in advance the number and type of data categories and data instances that will be received as the data is queried live from the sources. While developing Mobile Facets, we have applied a participatory design with a small group of five users. For the final prototype we have conducted a task-based, formative evaluation with 12 additional subjects to investigate the applicability and usability of our Mobile Facets application.     

Impact of Si on Microstructure and Mechanical Properties of 22MnB5 Hot Stamping Steel Treated by Quenching & Partitioning (Q&P)

Based on 22MnB5 hot stamping steel, three model alloys containing 0.5, 0.8, and 1.5 wt pct Si were produced, heat treated by quenching and partitioning (Q&P), and characterized. Aided by DICTRA calculations, the thermal Q&P cycles were designed to fit into industrial hot stamping by keeping partitioning times ≤ 30 seconds. As expected, Si increased the amount of retained austenite (RA) stabilized after final cooling. However, for the intermediate Si alloy the heat treatment exerted a particularly pronounced influence with an RA content three times as high for the one-step process compared to the two-step process. It appeared that 0.8 wt pct Si sufficed to suppress direct cementite formation from within martensite laths but did not sufficiently stabilize carbon-soaked RA at higher temperatures. Tensile and bending tests showed strongly diverging effects of austenite on ductility. Total elongation improved consistently with increasing RA content independently from its carbon content. In contrast, the bending angle was not impacted by high-carbon RA but deteriorated almost linearly with the amount of low-carbon RA.