Axial dispersion in metal foams and streamwise-periodic porous media

We present a study on the axial dispersion in metal foams and laser sintered reactors. Commercially available metal foams of 20 and 30 ppi are compared to a designed streamwise-periodic structure in terms of axial dispersion coefficients and pressure drops. Therefore tracer pulse experiments were performed and post processed by means of a deconvolution method. The Peclet number Pe_p based on the pore size is ranging from 5×10⁴ to 8×10⁵ which is attributed to the increased velocities due to the high porosity of the material compared to fixed bed reactors. The attained dispersion coefficients ranging from 1.3×10⁻⁴ to demonstrate the trend of packed beds and common packing materials and increase monotone with the Peclet number Pe_p. The pressure drop versus the interstitial bulk velocity follows the Forchheimer equation and can be described by the conventional Ergun model for all investigated porous media. The parameters obtained correspond to values found in literature. The results of this study show the high potential of foam reactors for catalyst driven reactions. They provide the same or even a higher surface area per volume of catalyst bed while inducing a much smaller pressure drop than corresponding fixed beds.     

Analysis of Phase Separation in High Performance PbTe–PbS Thermoelectric Materials

Phase immiscibility in PbTe–based thermoelectric materials is an effective means of top‐down synthesis of nanostructured composites exhibiting low lattice thermal conductivities. PbTe_1‐x S_x thermoelectric materials can be synthesized as metastable solid solution alloys through rapid quenching. Subsequent post‐annealing induces phase separation at the nanometer scale, producing nanostructures that increase phonon scattering and reduce lattice thermal conductivity. However, there has yet to be any study investigating in detail the local chemical structure of both the solid solution and nanostructured variants of this material system. Herein, quenched and annealed (i.e., solid solution and phase‐separated) samples of PbTe–PbS are analyzed by in situ high‐resolution synchrotron powder X‐ray diffraction, solid‐state ¹²⁵Te nuclear magnetic resonance (NMR), and infrared (IR) spectroscopy analysis. For high concentrations of PbS in PbTe, e.g., x >16%, NMR and IR analyses reveal that rapidly quenched samples exhibit incipient phase separation that is not detected by state‐of‐the‐art synchrotron X‐ray diffraction, providing an example of a PbTe thermoelectric “alloy” that is in fact phase inhomogeneous. Thermally‐induced PbS phase separation in PbTe–PbS occurs close to 200 °C for all compositions studied, and the solubility of the PbS phase in PbTe at elevated temperatures >500 °C is reported. The findings of this study suggest that there may be a large number of thermoelectric alloy systems that are phase inhomogeneous or nanostructured despite adherence to Vegard's Law of alloys, highlighting the importance of careful chemical characterization to differentiate between thermoelectric alloys and composites.     

Characterization of a cotton-wool like composite bone graft material

Bone graft materials are applied in patients to augment bone defects and enable the insertion of an implant in its ideal position. However, the currently available augmentation materials do not meet the requirements of being completely resorbed and replaced by new bone within 3 to 6 months. A novel electrospun cotton-wool like material (Bonewool^®, Zurich Biomaterials LLC, Zurich, Switzerland) consisting of biodegradable poly(lactic-co-glycolic) acid (PLGA) fibers with incorporated amorphous ß-tricalcium phosphate (ß-TCP) nanoparticles has been compared to a frequently used bovine derived hydroxyapatite (Bio-Oss^®, Geistlich Pharma, Wolhusen, Switzerland) in vitro. The material composition was determined and the degradation behavior (calcium release and pH in different solutions) as well as bioactivity has been measured. Degradation behavior of PLGA/ß-TCP was generally more progressive than for Bio-Oss^®, indicating that this material is potentially completely resorbable.

Graphical abstract

     

Brittle fracture in iridium

Brittle fracture in fcc metals is uncommon. It is not common knowledge that single crystals of iridium, a high melting point fcc metal, fail by brittle cleavage at room temperature. Furthermore, polycrystalline iridium fails predominantly by brittle inter granular fracture at temperatures below 1000°C. With the aid of several models of brittle fracture we have demonstrated that cleavage in iridium is intrinsic, resulting from apparently very strong and directed atomic binding forces. Intergranular fracture in iridium has been generally assumed to arise from the segregation of harmful impurities to the grain boundaries. We were able to demonstrate using Auger electron spectroscopy that impurity segregation to grain boundaries in iridium was not necessary for grain boundary fracture to occur, thereby demonstrating that intergranular brittle fracture in polycrystalline iridium is also intrinsic and not impurity related.     

Questionability of drift-diffusion transport in the analysis of small semiconductor devices

Analysis and design of such semiconductor devices as bipolar and field-effect transistors now relies, in part, on the assumption that current flows by drift and diffusion. The minute size of existing devices raises questions about the appropriateness of this assumption, however, because an internal region critical to device performance may become so small that carriers crossing it fail to experience many collisions. To demonstrate possible consequences of continuing to base analysis on assumed drift and diffusion, we contrast the predictions of two models for the electrical base region of a bipolar transistor. The first model assumes that carriers in transit across the base will experience many collisions, which requires a base region of sufficiently large dimensions. The second model assumes that a carrier in transit will suffer no collisions, displaying what tends to occur in the limiting case of small dimensions. A comparison of saturation current, temperature dependence, and base transit time shows that significant differences exist.     

Elastic registration of electrophoresis images using intensity information and point landmarks

A key technique for protein analysis is the geometric alignment of gel electrophoresis images. While in previous work either intensity- or landmark-based approaches have been used for the registration of electrophoresis images, we here introduce a scheme incorporating both intensity and landmark information. With this approach, point landmarks are localized using a model fitting scheme and this geometric information is combined with intensity information for elastic image registration. By experiments on the basis of electrophoresis images of different levels of complexity, we demonstrate that the intensity information alone is generally not sufficient to accurately register corresponding images. However, it turns out that the incorporation of landmarks significantly improves the registration accuracy. This is supported by quantitative results.     

Bildung von Mizellen aus ionogenen Tensidmolekülen Deutung des Minimums der Oberflächenspannungskurven

Formation of Micelles from Ionogenic Surfactant Molecules – Interpretation of the Minimum in Surface Tension Curves Surface tensions of surfactant solutions exhibit minimum values at a critical concentration. This phenomenon is interpreted as a result of oversaturation caused by aggregation of free surfactant molecules into micelles. An analogy to the condensation of water vapour molecules into water drops is demonstrated.     

NGN, All-IP, B3G: Enabler für das Future Net?!

Unterschiedliche Vorstellungen und Begriffe prägen gegenwärtig die Vorstellungen und Visionen über die Weiterentwicklung des Internets. Forschungsund Entwicklungsarbeiten in Richtung Future Net werden unter Bezeichnungen wie NGN, all-IP oder aber auch B3G (beyond 3G Networks) durchgeführt.