The Role of Chemically Innocent Polyanions in Active,Chemically Fueled Complex Coacervate Droplets

Complex coacervation describes the liquid-liquid phase separation of oppositely charged polymers. Active coacervates are droplets in which one of the electrolyte's affinity is regulated by chemical reactions. These droplets are particularly interesting because they are tightly regulated by reaction kinetics. For example, they serve as a model for membraneless organelles that are also often regulated by biochemical transformations such as post-translational modifications. They are also a great protocell model or could be used to synthesize life–they spontaneously emerge in response to reagents, compete, and decay when all nutrients have been consumed. However, the role of the unreactive building blocks, e.g., the polymeric compounds, is poorly understood. Here, we show the important role of the chemically innocent, unreactive polyanion of our chemically fueled coacervation droplets. We show that the polyanion drastically influences the resulting droplets′ life cycle without influencing the chemical reaction cycle–either they are very dynamic or have a delayed dissolution. Additionally, we derive a mechanistic understanding of our observations and show how additives and rational polymer design help to create the desired coacervate emulsion life cycles.     

Compact RGBY light sources with high luminance for laser display applications

Watt-class visible laser light with a high luminance can be created with high-power GaAs-based lasers either directly in the red spectral region or using single-pass second harmonic generation (SHG) for the colors in the blue–yellow spectral region. The concepts and results of red- and near infrared-emitting distributed Bragg reflector tapered lasers and master oscillator power amplifier systems as well as their application for SHG bench-top experiments and miniaturized modules are presented. Examples of these high-luminance light sources aiming at different applications such as flying spot display or holographic 3D cinema are discussed in more detail. The semiconductor material allows an easy adaptation of the wavelength allowing techniques such as six-primary color 3D projection or color space enhancement by adding a fourth yellow color.     

Passive mode locking of Yb:KLuW using a single-walled carbon nanotube saturable absorber

Mode locking of an Yb-doped bulk laser in the 1 microm spectral range using a single-walled carbon nanotube saturable absorber (SWCNT-SA) is demonstrated for the first time, to our knowledge. Passive mode locking of an Yb:KLuW laser resulted in nearly transform-limited pulses as short as 115 fs at 1048 nm. In addition, the nonlinear response of the SWCNT-SA was measured, yielding a modulation depth of 0.25% and a relaxation time of 750 fs.     

Self-sustained magnetoelectric oscillations in magnetic resonant tunneling structures

The dynamic interplay of transport, electrostatic, and magnetic effects in the resonant tunneling through ferromagnetic quantum wells is theoretically investigated. It is shown that the carrier-mediated magnetic order in the ferromagnetic region not only induces, but also takes part in intrinsic, robust, and sustainable high-frequency current oscillations over a large window of nominally steady bias voltages. This phenomenon could spawn a new class of quantum electronic devices based on ferromagnetic semiconductors.     

Adaptive nonlinear model predictive control design of a flexible-link manipulator with uncertain parameters

This paper presents a novel adaptive nonlinear model predictive control design for trajectory tracking of flexible-link manipulators consisting of feedback lineariza-tion, linear model predictive control, and unscented Kalman filtering. Reducing the nonlinear system to a linear system by feedback linearization simplifies the optimization prob-lem of the model predictive controller significantly, which, however, is no longer linear in the presence of parame-ter uncertainties and can potentially lead to an undesired dynamical behaviour. An unscented Kalman filter is used to approximate the dynamics of the prediction model by an online parameter estimation, which leads to an adaptation of the optimization problem in each time step and thus to a better prediction and an improved input action. Finally, a detailed fuzzy-arithmetic analysis is performed in order to quantify the effect of the uncertainties on the control structure and to derive robustness assessments. The control structure is applied to a serial manipulator with two flexible links containing uncertain model parameters and acting in three-dimensional space.     

The First Vanadium Oxide Nanotubes Containing an Aromatic Amine as Template

A new vanadate has been prepared in high yield by reacting vanadium(V) triisopropoxide and 3‐phenylpropylamine in solution, followed by hydrolysis and hydrothermal treatment of the intermediate product. For the first time, an aromatic amine has successfully been applied as structure‐directing template for the synthesis of vanadium oxide nanotubes. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images demonstrate the tubular morphology of the phenylpropylamine vanadium oxide nanotubes obtained. The size and structure are similar to that of vanadium oxide nanotubes formed with aliphatic amines. The tube walls comprise layers of vanadium oxide with the organic template intercalated in between. The interlayer distance is ca. 2.1 nm, and the structure of the VO_x layers can be described by a square lattice with a≈0.61 nm. Furthermore, the TEM investigation has revealed the presence of many defects in the wall structure.     

Synthetic control over polymorph formation in the d-band semiconductor system FeS2

Pyrite, also known as fool''s gold is the thermodynamic stable polymorph of FeS₂. It is widely considered as a promising d-band semiconductor for various applications due to its intriguing physical properties. Marcasite is the other naturally occurring polymorph of FeS₂. Measurements on natural crystals have shown that it has similarly promising electronic, mechanical, and optical properties as pyrite. However, it has been only scarcely investigated so far, because the laboratory-based synthesis of phase-pure samples or high quality marcasite single crystal has been a challenge until now. Here, we report the targeted phase formation via hydrothermal synthesis of marcasite and pyrite. The formation condition and phase purity of the FeS₂ polymorphs are systematically studied in the form of a comprehensive synthesis map. We, furthermore, report on a detailed analysis of marcasite single crystal growth by a space-separated hydrothermal synthesis. We observe that single phase product of marcasite forms only on the surface under the involvement of H₂S and sulphur vapor. The availability of high-quality crystals of marcasite allows us to measure the fundamental physical properties, including an allowed direct optical bandgap of 0.76 eV, temperature independent diamagnetism, an electronic transport gap of 0.11 eV, and a room-temperature carrier concentration of 4.14 × 10¹⁸ cm⁻³. X-ray absorption/emission spectroscopy are employed to measure the band gap of the two FeS₂ phases. We find marcasite has a band gap of 0.73 eV, while pyrite has a band gap of 0.87 eV. Our results indicate that marcasite – that is now synthetically available in a straightforward fashion – is as equally promising as pyrite as candidate for various semiconductor applications based on earth abundant elements.

Pyrite, also known as fool''s gold is the thermodynamic stable polymorph of FeS₂.     

Determination of the Effective Vacancy Concentrations and the Vacancy Losses after the Quench of Al–Zn–Mg Alloys

On the basis of

• 1 the experimental observation of dislocation loops by means of TEM,
• 2 the conclusion from this that the concentration of vacancies in the dislocation loops exists at the cost of the vacancy concentration primarily present at T_q, and
• 3 the inversion of the decomposition kinetics of Al–Zn–Mg alloys found out by means of resistivity and microhardness measurements, the effective vacancy concentration c_v.eff being at disposal for the GP-zone formation was found out by means of the relation t_R,max (t_R,max being the time required to reach the maximum of resistivity) and the Arrhenius plot In t_R,max = f(1/T_q) of the isothermal resistivity measurements. From the comparison of c_v.eff with the theoretical V concentration at T_q it is possible to derive statements about the loss of vacancies during and after the quench through loop formation, building-in of vacancies in GP-zones and annealing of vacancies at lattice defects. From this comparison follows:
  • The ideal ZnV concentration at T_q (calculated by means of the Lomer equation) is sufficiently great to account for the effective vacancy concentration.
  • The part of c_MgV in the loss concentration is rising with increasing c_Mg.
  Both these statements support the hypothesis that the initial process of the decomposition in Al–Zn–Mg alloys is caused by the ZnV diffusion.