Syntheses of intrinsically flame-retardant polyamide 6 fibers and fabrics

In this study, flame-retarded polyamide 6 (FR-PA6) was prepared via the direct co-condensation of ε-caprolactam with two different organophosphorus compounds in a typical melt-polymerization process. Polymer microstructures, especially the incorporation of the phosphorus-containing comonomers, as well as the thermal and physical properties of the resulting copolyamides have been studied in detail. The phosphorus-modified PAs have a P-content of 0.10–0.30 wt %, possess high relative viscosities of 2.2–2.4 and good thermal stability. FR-PA6 multifilaments were prepared by melt spinning and show tensile strengths up to 40 cN/tex and tenacities up to 0.5 GPa. Knitted fabrics of FR-PA6 exhibit high limiting oxygen index values around 35%. Due to the very low phosphorus content, there is no impairment of the material properties of PA6. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47829.     

Improving single-mode VCSEL performance by introducing a longmonolithic cavity

We report on the improvement of several selectively oxidized vertical-cavity surface emitting laser characteristics by introducing a long monolithic cavity. The samples compared are grown with various cavity lengths using solid-source MBE. The 980 nm-regime is chosen as emission wavelength to facilitate growth by using binary GaAs cavity spacers. A record high single-transverse mode output power of 5 mW at a series resistance of 98 Ω is obtained for a 7-μm aperture device with a 4-μm cavity spacer. Using an 8-μm cavity spacer, devices up to 16-μm aperture diameter emit 1.7 mW of single-mode power with a full-width at half-maximum far-field angle below 3.8°     

High-power VCSELs: single devices and densely packed 2-D-arrays

We report on vertical-cavity surface-emitting lasers (VCSELs) and laser arrays providing high output powers in the 980-nm wavelength regime. Extensive investigations on size scaling behavior of single top- and bottom-emitting devices concerning fundamental electrooptical and thermal properties show limits of attainable output characteristics. Maximum experimentally achieved continuous-wave (CW) optical output powers at room temperature are 180 and 350 mW for top- and bottom-emitting VCSELs, respectively. Detailed analysis on the thermal interaction between closely spaced elements have been carried out to describe the thermally induced power limitations of two-dimensional arrays. Fabricated heat sunk bottom-emitting arrays of 23 elements and 40-μm aperture size of individual elements show output powers of 0.56 W CW at room temperature and 0.8 W actively cooled, resulting in 0.33 kW/cm² and 0.47 kW/cm² maximum spatially averaged optical power density, respectively     

The influence of Na on low temperature growth of CIGS thin film solar cells on polyimide substrates

The objective of this work is to study the influence of Na on the properties of Cu(In,Ga)Se₂ (CIGS) absorber layers and finished solar cell devices on polyimide substrates. For this study Na is added to 3-stage grown CIGS thin films by evaporation of a NaF precursor layer prior to the absorber deposition. The precursor layer modifies the CIGS growth kinetics. A stronger Ga-gradient and a decrease of grain size are observed when the Na content increases. An increase in V_oc for a higher Na concentration at a nominal growth temperature of T_sub,max = 500 °C during CIGS deposition is explained by a higher carrier density, as obtained by DLCP measurements. The higher carrier concentration for the higher Na content could be attributed to the reduction of a compensating donor. However, a low J_sc does not allow for an enhanced efficiency possibly due to a shorter depletion region, as observed by admittance spectroscopy, and effective diffusion length.     

Self-adaptation of learning rate in XCS working in noisy and dynamic environments

An extended classifier system (XCS) is an adaptive rule-based technique that uses evolutionary search and reinforcement learning to evolve complete, accurate, and maximally general payoff map of an environment. The payoff map is represented by a set of condition-action rules called classifiers. Despite this insight, till now parameter-setting problem associated with LCS/XCS has important drawbacks. Moreover, the optimal values of some parameters are strongly influenced by properties of the environment like its complexity, changeability, and the level of noise. The aim of this paper is to overcome some of these difficulties by a self-adaptation of a learning rate parameter, which plays a key role in reinforcement learning, since it is used for updates of classifier parameters: prediction, prediction error, fitness, and action set estimation. Self-adaptive control of prediction learning rate is investigated in the XCS, whereas the fitness and error learning rates remain fixed. Simultaneous self-adaptation of prediction learning rate and mutation rate also undergo experiments. Self-adaptive XCS solves one-step problems in noisy and dynamic environments.     

Polarisation control in VCSELs by elliptic surface etching

850 nm-wavelength vertical-cavity surface-emitting lasers (VCSELs) with an elliptical shallow surface relief having various aspect ratios and orientations have been fabricated. Using appropriate etch dimensions, VCSELs of up to 12.5 μm active diameter are forced to operate on the fundamental mode for a certain current range. By aligning the longer axis of the etched ellipse with the [011] or [011¯] crystal axis, the polarisation of the fundamental mode is pinned accordingly with a polarisation suppression ratio of ~30 dB