Biosynthetic Plasticity Enables Production of Fluorinated Aurachins

Enzyme promiscuity has important implications in the field of biocatalysis. In some cases, structural analogues of simple metabolic building blocks can be processed through entire pathways to give natural product derivatives that are not readily accessible by chemical means. In this study, we explored the plasticity of the aurachin biosynthesis pathway with regard to using fluoro- and chloroanthranilic acids, which are not abundant in the bacterial producers of these quinolone antibiotics. The incorporation rates of the tested precursor molecules disclosed a regiopreference for halogen substitution as well as steric limitations of enzymatic substrate tolerance. Three previously undescribed fluorinated aurachin derivatives were produced in preparative amounts by fermentation and structurally characterized. Furthermore, their antibacterial activities were evaluated in comparison to their natural congener aurachin D.     

Correction to: Co-sputtering of Al1−xScxN thin films on Pt(111): a characterization by Raman and IR spectroscopies

Journal of Materials Science -     

Modeling and in-depth analysis of the start-up of dividing-wall columns

Saving potentials of up to 30% in capital and operating costs are the driving forces behind the increase in the application of dividing-wall columns in industry. However, a lack of knowledge still exists when dealing with the start-up of dividing-wall columns, which is inherently a strongly nonlinear process. Here, for the first time the start-up of dividing-wall columns is explored, where the starting point is an empty column at ambient conditions. A model is presented which is capable of predicting the dynamic discrete-continuous changes which are characteristic of dividing-wall columns. The proposed process model takes into account the heat transfer across the dividing wall as well as the vapor distribution below the dividing wall. The degree of accuracy of the model is clearly determined by comparing different simplifications, e.g. a constant vapor distribution ratio equal to the steady-state value. The detailed studies were carried out with strict product specifications so that the influence of process parameters could be quantified. The rigorous process model and the obtained simulation results presented in this study provide a promising basis for developing and applying optimal start-up policies for dividing-wall columns.     

Carbon‐Based Anodes for Lithium Sulfur Full Cells with High Cycle Stability

The lithium sulfur battery system has been studied since the late 1970s and has seen renewed interest in recent years. However, even after three decades of intensive research, prolonged cycling can only be achieved when a large excess of electrolyte and lithium is used. Here, for the first time, a balanced and stable lithium sulfur full cell is demonstrated with silicon–carbon as well as all‐carbon anodes. More than 1000 cycles, a specific capacity up to 1470 mAh g^?1 _sulfur (720 mAh g^?1 _cathode), and a high coulombic efficiency of over 99% even with a low amount of electrolyte are achieved. The alternative anodes do not suffer from electrolyte depletion, which is found to be the main cause of cell failure when using metallic lithium anodes.     

Energy Offset Between Silicon Quantum Structures: Interface Impact of Embedding Dielectrics as Doping Alternative

Ultrasmall silicon (Si) nanoelectronic devices require an energy shift of electronic states for n‐ and p‐conductivity. Nanocrystal self‐purification and out‐diffusion in field effect transistors cause doping to fail. Here, it is shown that silicon dioxide (SiO₂) and silicon nitride (Si₃N₄) create energy offsets of electronic states in embedded Si quantum dots (QDs) in analogy to doping. Density functional theory (DFT), interface charge transfer (ICT), and experimental verifications arrive at the same size of QDs below which the dielectric dominates their electronic properties. Large positive energy offsets of electronic states and an energy gap increase exist for Si QDs in Si₃N₄ versus SiO₂. Using DFT results, the SiO₂/QD interface coverage is estimated with nitrogen (N) to be 0.1 to 0.5 monolayers (ML) for samples annealed in N₂ versus argon (Ar). The interface impact is described as nanoscopic field effect and propose the energy offset as robust and controllable alternative to impurity doping of Si nanostructures.     

Influence of Compaction Conditions on the Foamability of AlSi8Mg4 Alloy

Aluminum AlSi8Mg4 alloy foams were produced by the powder compact foaming route using different parameters for the uniaxial powder compaction step. Compaction time, pressure, and temperature were varied and were found to influence both the density of the foamable precursor and the peak expansion reached during foaming. While peak expansion cannot be related to any single pressing parameter alone in a simple way, a clear dependence of expansion on the precursor density was found. Densification to a relative density between 97.5 and 99 pct yielded volume expansions of the foam up to 880 pct. Lower densities result in weaker foaming, due to insufficient encapsulation of the blowing agent; in addition, we were surprised to find that higher densification also has an adverse effect on peak expansion, most likely due to the elimination of nucleation centers or the effect of entrapped compressed air. Precursor microstructures were analyzed to identify the mechanisms leading to the observed density dependence of expansion.     

Coefficient of Friction Measurements for Thermoplastics and Fibre Composites Under Low Sliding Velocity and High Pressure

Friction materials for typical brake applications are normally designed considering thermal stability as the major performance criterion. There are, however, brake applications with very limited sliding velocities, where the generated heat is insignificant. In such cases it is possible that friction materials which are untypical for brake applications, like thermoplastics and fibre composites, can offer superior performance in terms of braking torque, wear resistance and cost than typical brake linings. In this paper coefficient of friction measurements for various thermoplastic and fibre composite materials running against a steel surface are presented. All tests were carried out on a pin-on-disc test-rig in reciprocating operation at a fixed sliding speed and various pressure levels for both dry and grease lubricated conditions. Moreover, a generic theoretical framework is introduced in order to interpret the changes of friction observed during the running-in phase.     

Modeling temperature distribution in rigid pavement slabs: Impact of air temperature

This study presents the impact of air temperature on the temperature distributions through the depth of rigid pavement slabs. A one-dimensional heat transfer model is proposed to predict the temperature distribution across the pavement. To highlight the impact of daily temperature amplitude on a pavement temperature profiles, the summer weather condition is used as an input to simulate the temperature distributions through slabs in mountainous desert and coastal regions. The results section presents the impact of daily ambient temperature on the pavement-surface heat exchange and subsequent slab temperature development. The feasibility of using the sinusoidal-approximated air temperature is also described. The subsequent discussion concentrates on whether the predicted results of these two regions can be used to develop similar conclusions in other regions and other seasons. The discussion also focuses on the boundary-formulation differences between the proposed model and the documented temperature prediction models for concrete slabs.     

Applying Model Predictive Control to Dividing Wall Columns

The technology of dividing wall columns can offer enormous energy savings compared to common distillation columns and configurations. The technology of model predictive control is also advantageous since such a controller minimizes the future deviation of the predicted controlled variable from the reference point. The practical application of model predictive controllers for dividing wall columns is still limited due to limited experience with high interactions among the process variables. The scope of this work is the development and analysis of a method for the design of model predictive controllers for dividing wall columns. An experimental investigation verifies the practicability of the applied approach. The methods generated are transferable to other applications. Thus, the industrial acceptance of model predictive controllers for dividing wall columns is enhanced.