A non-autonomous optimal control model of renewable energy production under the aspect of fluctuating supply and learning by doing

Given the constantly raising world-wide energy demand and the accompanying increase in greenhouse gas emissions that pushes the progression of climate change, the possibly most important task in future is to find a carbon-low energy supply that finds the right balance between sustainability and energy security. For renewable energy generation, however, especially the second aspect turns out to be difficult as the supply of renewable sources underlies strong volatility. Further on, investment costs for new technologies are so high that competitiveness with conventional energy forms is hard to achieve. To address this issue, we analyze in this paper a non-autonomous optimal control model considering the optimal composition of a portfolio that consists of fossil and renewable energy and which is used to cover the energy demand of a small country. While fossil energy is assumed to be constantly available, the supply of the renewable resource fluctuates seasonally. We further on include learning effects for the renewable energy technology, which will underline the importance of considering the whole life span of such a technology for long-term energy planning decisions.     

A comparison of tools for teaching formal software verification

We compare four tools regarding their suitability for teaching formal software verification, namely the Frege Program Prover, the Key system, Perfect Developer, and the Prototype Verification System (PVS). We evaluate them on a suite of small programs, which are typical of courses dealing with Hoare-style verification, weakest preconditions, or dynamic logic. Finally we report our experiences with using Perfect Developer in class.     

通用运动控制技术

Gernot Bachler在贝加莱奥地利Eggelsberg总部从事运动控制的研发工作。 “设备厂商要的不只是简单的控制器,而是对设备自动化的完全掌控。这包括驱动器,电机（路径控制）,基于视觉和网络的组件。具有CNC功能块的路径控制会成为自动化控制的集成部分。贝加莱把所有这些组件集合到一个系统中,形成了一套崭新的方案。”     

Experimental analysis of the influence of pellet shape on single screw extrusion

Extrusion technology is one of the most prominent methods for processing polymers. The shape of polymer pellets plays an important role in conveying solid material through the extruder and thus directly influences the mass flow rate. In the course of this article, the influence of the pellet shape of a polypropylene homopolymer on the processing conditions using a smooth barrel single‐screw extruder is evaluated. Especially the mass flow rate, the melt temperature, and the pressure build up in the barrel are investigated. It can be shown that processing long cylindrical pellets leads to a higher mass flow rate than comparable experiments with virgin pellets or short cylinders. Additionally, screw cool and pull‐out tests, measurements of the external coefficient of friction as well as the bulk density of the different pellet geometries are performed. The interaction of the screw geometry and the pellet shape is found to have the biggest influence. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41716.     

Blast furnace slags as functional fillers on rheological,thermal, and mechanical behavior of thermoplastics

Blast furnace slags (BFS) is a secondary byproduct of iron industry, which has a combination of acidic and basic oxides and show a complex, multiphase structure. If appropriately tailored, BFS could be an effective functional filler, improving the property profile of thermoplastics such as polypropylene (PP) and polystyrene (PS). As a raw material, the proposed filler may introduce both economic and ecological advantages, as it is considered an inexpensive secondary product rather than a natural resource. The current study aims at investigating the effect of incorporating BFS as a micro‐sized filler on the rheological, thermal, and mechanical behavior of PP and PS. BFS types in this study are air‐cooled, crystalline, and amorphous, grounded types. Both types are ground into 71, 40, and 20 μm batches and introduced in 10, 20, and 30 weight fractions via melt kneading. Mixtures are then formed into 4‐mm and 2‐mm thick plates via compression molding. Slight increase in rheological factors is observed with increasing filler loading. BFS hinders the crystallization of PP, resulting in slight increase of crystallization temperatures (T_c) and lowering of crystallization enthalpy (ΔH_c). No significant effect of filler on transition temperatures (T_g) is reported. Mechanically, BFS increases the tensile modulus of PP, but decreases its strength. For PS formulations, a modest toughening effect is observed by slag filler. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43021.     

Tuning the Electronic Structure of Graphene through Collective Electrostatic Effects

Electrostatically designing materials opens a new avenue for realizing systems with user‐defined electronic properties. Here, an approach is presented for efficiently patterning the electronic structure of layered systems such as graphene by means of collective electrostatic effects. Using density‐functional theory simulations, it is found that lines of polar elements can strongly modify the energy landscape of this prototypical 2D material. This results in a confinement of electronic states in specific regions of the sample and, consequently, in a local energetic shift of the density of states. The latter is also directly reflected in the details of the band structure of the electrostatically patterned sample. Finally, it is shown that the approach can also be successfully applied to other 2D materials such as hexagonal boron nitride, where the effects are predicted to be even more pronounced than in graphene.     

Correlation of the loss in photovoltaic module performance with the ageing behaviour of the backsheets used

The influence of the type of backsheet on the electrical performance of test modules was evaluated before and after increasing time of accelerated ageing (damp heat [DH] exposure). Besides the measurement of the electrical power of the modules and the performance of the cells by electroluminescence, the ageing‐induced changes within the polymeric encapsulate and backsheets were investigated by means of vibrational spectroscopy and by thermo analytical methods. In addition, the permeability of the backsheets in the original and aged state was determined. This wide set of test parameters and methods allowed for the detection of correlations between (i) physical and chemical properties as well as their ageing‐induced changes of the materials and (ii) the module performance. A clear dependence of the relative loss in power output upon exposure under DH conditions for 2000 h could be observed for a set of identical test modules varied in composition only in the type of back cover used. While the modules containing gas‐tight backsheets and glass experienced only little loss in the relative power output, some modules with permeable backsheets showed a significant relative decrease in the power output and fill factor in dependence of the backsheet type used. Cell degradation could be visualised by recording electroluminescence images before and after the accelerated ageing test. The permeation properties of the backsheet used and their ageing‐induced changes seem to have an influence on the module performance. However, the absolute values neither of the water vapour transmission rate (WVTR) nor of the oxygen transmission rate (OTR) are directly linked to the loss in power output upon accelerated ageing under DH conditions. It could be shown that the ageing‐induced changes (relative transmission rates) between WVTR and OTR can be correlated with the module performance. These ageing‐induced changes in the permeation behaviour of the backsheets can be explained by (i) physical changes (e.g. post‐crystallisation, changes in the crystal structure or the crystalline microstructure) and (ii) chemical ageing effects such as a decrease in the molecular mass of the polyester (PET) polymer chains because of hydrolytic polymer degradation leading to a change in the crystallisation behaviour of PET. Hydrolytic degradation (= chemical ageing) of the PET core layer was observed (with varying extent) for all PET‐based backsheets and can, thus, not be directly correlated with the loss in performance of the corresponding test modules. The physical ageing effects, however, were detected only for those backsheets showing (i) strong deviating changes in the relative permeation rates for oxygen and water vapour upon accelerated ageing and (ii) a clear loss in electrical performance. Copyright © 2015 John Wiley & Sons, Ltd.