A physical explanation of the gas flow diode effect

Gas flow properties in channels with slightly varying cross section have a dependency on the direction of channel perfusion when the gas is in the slip and transitional flow regimes. In the past, it was observed that the flow rate in converging direction is higher compared to the case where the channel diverges alongside. This gas flow diode effect does neither exist in the continuum regime nor in the free molecular regime, and it has its maximum at the same level of gaseous rarefaction as the well-known Knudsen minimum. However, no comprehensive study on the physics of this diode effect is carried out yet. In order to overcome this knowledge gap, the current paper proceeds our previous works by an appropriate experimental study. Here we can show that the diode effect crucially depends on the proportion of inclined walls to the overall channel inner surface. Also the inclination of the wall itself determines the strength of the diode effect meaning that the diodicity increases with the opening angle. Furthermore, we found indication that the diodicity also depends on the molar mass and the internal structure of the impinging gas molecules. Finally, we propose an explanation of the diode effect that is mainly based on the tangential reflection process of gas molecules colliding with the inclined walls of a tapered channel.     

Deformation mechanism of aluminum–magnesium alloys at elevated temperatures

The study concentrates on the formulation of a reliable constitutive equation for plastic forming of Al–Mg-based alloys above 400 °C and at strain rates above 10^?3 s^?1. The deformation mechanisms of two coarse-grained Al–Mg alloys, also known as AA5182, with grain sizes 21 and 37 μm were investigated. They exhibited optimum extension at 10^?2 s^?1 and at T equal to 425 °C and above 475 °C, respectively, with uniform elongation above 300 %. The strain-rate sensitivity and the stress exponent were equal to 0.25 and 4, respectively, suggesting that the deformation is controlled by the solute drag of gliding dislocations whereas dislocation climb occurs also in grains whose orientation renders them hard. Grain boundary sliding may contribute to a small extent in the deformation process. The threshold stress was found to be small and the activation energy lies between 144 and 136 kJ mol^?1, i.e., that of Al self-diffusion and Mg diffusion in Al. It is concluded that coarse-grained materials may well fulfill the industrial requirements of forming and within this scope, the use of the low purity coarse-grained Al–Mg-based alloys of the AA5182 type would constitute the next step in the course for further cost reduction.     

Band-gap tuning of pendant polymers for organic light-emitting devices and photovoltaic applications

The preparation of a series of novel polymers comprising pendant electro-active “push–pull” chromophores and their performance in solution-processed organic electronic devices is described. The design of the electro-active pendant chromophores was based on the well-known motif of cyano-substituted poly(p-phenylenevinylene). Optical band-gap engineering within this series of polymers was achieved by varying the conjugation length and the electron donor/acceptor functionalities of the pendant chromophores. The introduction of a cyanoimine group into the electro-active pendant module resulted in a marked narrowing of the optical band-gap compared with the other electro-active pendant chromophores investigated in this work. Bulk heterojunction solar cell devices comprising these polymers were prepared by solution processing blends of each polymer with [6,6]-phenyl-C₆₁-butyric acid methyl ester, and their performance was evaluated by measuring power conversion efficiencies. The best-performing solar cell in this series exhibited a power conversion efficiency of 0.29% and a maximum incident photon-to-current conversion efficiency of 22% and was produced using the polymer in which the electro-active chromophore comprised the cyanoimine group.     

Effects of soluble surfactants on the Langmuir monolayers compressibility: A comparative study using interfacial isotherms and fluorescence microscopy

Langmuir monolayer isotherms and fluorescence microscopy (FM) techniques have been used to study the effect of two soluble surfactants on the methyl octadecanoate monolayer's compressibility at the air/water interface. The combination of these two techniques allows one to bridge the mechanical and morphological properties of the monolayer at different surfactant subphase concentrations. Our results show that the presence of sodium dodecyl sulfate (SDS) or dodecyltrimethylammonium bromide (DTAB) affects the monolayer elasticity differently. In addition, the outcome of this study emphasizes the role of the cationic and anionic surfactants on the monolayer compressibility. In fact, their effect was found to be primly depending on the monolayer thermodynamic situation. The isotherms of the monolayers at different surfactant concentrations underneath the monolayer preserve the characteristics behavior of the monolayer as imaged by FM. The calculated monolayer compressibility shows two different trends depending on the monolayer pressure and the surfactant type. A decreasing compressibility as a function of SDS concentration was found at pressure π = 5 mN/m, while no noticeable effect was found due to DTAB. At π = 10 mN/m both surfactants convert the monolayer from rigid to soft monolayer. Such characteristic behavior of the monolayer has been confirmed by FM.     

Target Costing für Werkstoffe – Potenziale und Methodik

Target Costing for Materials – Potentialities and Methodology Target Costing is a standard instrument of cost management in business administration, but hardly mentioned in the economic oriented literature on material sciences. Nevertheless there are high potentialities for developers, producers, or users of materials regarding the improvement of efficiency. Therefore, this article will present these potentialities of a material oriented Target Costing. Besides, the general methodology of Target Costing will be modified to meet the specifics of materials from the perspectives of users of materials on the one hand and developers respectively producers of materials on the other.     

具备更强机械性能的高功率IGBT模块——采用最新3．3kV IGBT3芯片技术

本文介绍了新一代IHM．B具备更强机械性能的高功率IGBT模块，其融合了最新的设计、材料、焊接和安装技术。首批IHMB模块将搭载最新的、采用沟槽栅单元设计的3．3kV IGBT3芯片，在保持机械兼容性的同时，极大地提高了器件的热效率和电气效率。本文还对宇宙射线以及功率循环试验进行了研究。