Influence of Electron Beam Powder Bed Fusion Process Parameters at Constant Volumetric Energy Density on Surface Topography and Microstructural Homogeneity of a Titanium Aluminide Alloy

In powder bed fusion additive manufacturing, the volumetric energy density E _V is a commonly used parameter to quantify process energy input. However, recent results question the suitability of E _V as a design parameter, as varying the contributing parameters may yield different part properties. Herein, beam current, scan velocity, and line offset in electron beam powder bed fusion (PBF-EB) of the titanium aluminide alloy TNM–B1 are systematically varied while maintaining an overall constant E _V. The samples are evaluated regarding surface morphology, relative density, microstructure, hardness, and aluminum loss due to evaporation. Moreover, the specimens are subjected to two different heat treatments to obtain fully lamellar (FL) and nearly lamellar (NLγ) microstructures, respectively. With a combination of low beam currents, low-to-intermediate scan velocities, and low line offsets, parts with even surfaces, relative densities above 99.9%, and homogeneous microstructures are achieved. On the other hand, especially high beam currents promote the formation of surface bulges and pronounced aluminum evaporation, resulting in inhomogeneous banded microstructures after heat treatment. The results demonstrate the importance of considering the individual parameters instead of E _V in process optimization for PBF-EB.     

Correlation of EPS content in activated sludge at different sludge retention times with membrane fouling phenomena

In this study, activated sludge characteristics were studied with regard to membrane fouling in membrane bioreactors (MBRs) for two pilot plants and one full-scale plant treating municipal wastewater. For the full-scale MBR, concentrations of extracellular polymeric substances (EPS) bound to sludge flocs were shown to have seasonal variations from as low as 17mgg(-1) dry matter (DM) in summer up to 51mg(gDM)(-1) in winter, which correlated with an increased occurrence of filamentous bacteria in the colder season. Therefore, it was investigated at pilot-scale MBRs with different sludge retention times (SRTs) whether different EPS contents and corresponding sludge properties influence membrane fouling. Activated sludge from the pilot MBR with low SRT (23d) was found to have worse filterability, settleability and dewaterability. Photometric analysis of EPS extracts as well as LC-OCD measurements showed that it contained significantly higher concentrations of floc-bound EPS than sludge at higher SRT (40d) The formation of fouling layers on the membranes, characterised by SEM-EDX as well as photometric analysis of EPS extracts, was more distinct at lower SRT where concentrations of deposited EPS were 40-fold higher for proteins and 5-fold higher for carbohydrates compared with the membrane at higher SRT. Floc-bound EPS and metals were suggested to play a role in the fouling process at the full-scale MBR and this was confirmed by the pilot-scale study. However, despite the different sludge properties, the permeability of membranes was found to be similar.     

Knowledge environments representing molecular entities for the virtual physiological human

In essence, the virtual physiological human (VPH) is a multiscale representation of human physiology spanning from the molecular level via cellular processes and multicellular organization of tissues to complex organ function. The different scales of the VPH deal with different entities, relationships and processes, and in consequence the models used to describe and simulate biological functions vary significantly. Here, we describe methods and strategies to generate knowledge environments representing molecular entities that can be used for modelling the molecular scale of the VPH. Our strategy to generate knowledge environments representing molecular entities is based on the combination of information extraction from scientific text and the integration of information from biomolecular databases. We introduce @neuLink, a first prototype of an automatically generated, disease-specific knowledge environment combining biomolecular, chemical, genetic and medical information. Finally, we provide a perspective for the future implementation and use of knowledge environments representing molecular entities for the VPH.     

Field-dependent DNA mobility in 20 nm high nanoslits

The transport behavior of lambda-DNA (48 kbp) in fused silica nanoslits is investigated upon application of electrical fields of different strengths. The slit dimensions are 20 nm in height, 3 microm in width, and 500 microm in length. With fields of 30 kV/m or below, the molecules move fluently through the slits, while at higher electrical fields, the DNA molecules move intermittently, resulting in a strongly reduced mobility. We propose that the behavior can be explained by mechanical and/or field-induced dielectrophoretic DNA trapping due to the surface roughness in the nanoslits. The observation of preferential pathways and trapping sites of the lambda-DNA molecules through the nanoslits supports this hypothesis and indicates that the classical viscous friction models to explain the DNA movement in nanoslits needs to be modified to include these effects. Preliminary experiments with the smaller XbaI-digested litmus-DNA (2.8 kbp) show that the behavior is size-dependent, suggesting that the high field electrophoresis in nanoslits can be used for DNA separation.     

Optically monitored segmented flow for controlled ultra-fast mixing and nanoparticle precipitation

Nanoparticles of drugs or colloidal carrier systems are capable of providing substantial advantages for drug bioavailability, but manufacturing nanoparticulate drugs or drug carriers remains a challenge because traditional mechanical or chemical batch mode processes might lack precise control of nanoparticle sizes. Microfluidic approaches are believed to give advantages but often do not provide chemically inert environments and lack controllable operation. Here, segmented flow devices with symmetrical design for centered organic phase injection and for nanoparticle precipitation in transparent and chemically inert glass microchannels are presented. Femtosecond laser fabrication was used to structure borosilicate glass wafers with hydrophilic microchannels of nearly circular cross section. They allow for ultra-fast mixing of solvents with aqueous fluids and subsequent precipitation of poorly water soluble drug nanoparticles or colloidal carrier particles. The best results for mixing and controlled precipitation were obtained with flow focusing and gas segmentation occurring at the same channel intersection point. In such systems, early interdiffusion of the solvent and aqueous solution before ultra-fast convective mixing in the plug is suppressed. A novel optical analysis technique revealed that the speed of mixing can be well controlled by simply adjusting the volume flow rate of the gas phase where changes in the liquid flow rate have practically no influence. In a controlled and stable Taylor flow, smallest plug volumes of 3.8 nl can be generated, which allows complete mixing in 9 ms. The production of lipid nanoparticles down to a diameter of 74 nm could already be demonstrated.     

Multiplex PCR for the simultaneous detection of Salmonella spp. and Salmonella Enteritidis in food

Multiplex PCR assay (mPCR) for the detection of Salmonella spp. and S. Enteritidis was developed in this study using artificially contaminated chicken carcasses. The assay showed 100% specificity to detect approximately 1 CFU of Salmonella in 10 g of chicken skin after non‐selective enrichment. The mPCR was evaluated in Minas cheese, fresh pork sausage and chicken carcasses commercially available. Salmonella spp. was detected in nine of sixty‐six chicken carcasses, five of fifty‐two cheese samples, and five of fifty‐two sausage samples. The serovar Enteritidis was detected in two samples of contaminated sausage. The mPCR results were confirmed by conventional culture and biochemical identification of the isolates. Serotyping confirmed the presence of S. Enteritidis in sausage samples and showed contamination by serovars Schwarzengrund and Montevideo in chicken carcasses.     

New Polymer‐Supported Catalysts for the Asymmetric Transfer Hydrogenation of Acetophenone in Water – Kinetic and Mechanistic Investigations

Heterogenization is a powerful approach for the generation of easily recyclable catalysts. In this study, a modified tethered rhodium(III)‐ p‐toluenesulfonyl‐1,2‐diphenylethylenediamine (Rh‐TsDPEN) complex immobilized on polymeric supports was applied to kinetic and up‐scaling experiments on the asymmetric transfer hydrogenation of acetophenone in water. Study of the catalyst has helped in understanding some aspects of its operating mode. The results indicate that, in the investigated range, a simple second‐order model describes the enantioselective conversion of acetophenone to phenylethanol. Optimal reaction conditions were determined, and particularly the solution pH was found to play a decisive role for the activity and reusability of the catalyst. The good performance under optimized conditions emphasizes the practical usefulness of this recyclable catalytic system for environmentally benign asymmetric transfer hydrogenation processes.