Operating conditions of batteries in off-grid renewable energy systems

Operating conditions in off-grid renewable energy systems (RES) vary significantly in different applications and locations. To describe RES and the operating conditions of their components it is useful to define categories of similar operating conditions. Categories can also be used for lifetime considerations of RES components, for making recommendations and for analysing the properties and performance of a RES and its components. Categories support system designers and an economic analysis. This paper describes the process and the results of creating RES categories of similar operating conditions for batteries. Categories are defined in such a way that batteries belonging to the same category are subjected to similar operating conditions and a similar combination of stress factors. The results provide a comprehensive overview of battery operating conditions in existing off-grid renewable energy systems. This work is part of the EU research project Benchmarking.¹     

In-situ investigations of magnetron sputtering processes with laboratory X-ray equipment

An Fe-Al duplex film was prepared on a Si(111)-wafer by sputter deposition in a vacuum chamber with two integrated small magnetron sources. The chamber allows the in-situ investigation of such sputtering processes using grazing incidence X-ray reflectivity, X-ray scattering measurements and X-ray diffraction. We will present details of the new cell and present the first results obtained using reflectivity measurements of the Fe-Al thin films. Here we will focus on the detailed evaluation of the specular reflectivity data of the iron films only, which clearly indicates the presence of an iron oxide, the density and roughness of which were determined and their changes with the film thickness were discussed in the framework of thin film growth models.     

On the History of Reactive Mesogens: Interview with Dirk J. Broer

Prof. Dirk Broer is among the pioneers and most active researchers in the field of stimuli-responsive liquid crystal (LC) networks. He is the inventor of reactive mesogens, a class of materials with far-reaching implications in liquid-crystal photonics and in the triumph of LC-based shape-shifting polymers. Together with his team, Prof. Broer continuously produces innovative solutions for controlling and programming new functions into soft responsive materials. Through this Interview, it is our great pleasure to gain insights into his personal views on both the past and the future, and to learn about the historical turns that led to the development of reactive mesogens as well as his vision on where the field is heading.     

COBIT 2019: A SIGNIFICANT UPDATE

The new framework for governance and management of enterprise information & technology – COBIT 2019 – has been released. The updated framework provides a timely refresh of its structure and contents, and adds exciting new features like design factors that allow to tailor governance systems, and many more. This article describes the major changes in COBIT and the impact they bring to governing bodies, management and practitioners.     

Tomographic particle image velocimetry of desert locust wakes: instantaneous volumes combine to reveal hidden vortex elements and rapid wake deformation

Aerodynamic structures generated by animals in flight are unstable and complex. Recent progress in quantitative flow visualization has advanced our understanding of animal aerodynamics, but measurements have hitherto been limited to flow velocities at a plane through the wake. We applied an emergent, high-speed, volumetric fluid imaging technique (tomographic particle image velocimetry) to examine segments of the wake of desert locusts, capturing fully three-dimensional instantaneous flow fields. We used those flow fields to characterize the aerodynamic footprint in unprecedented detail and revealed previously unseen wake elements that would have gone undetected by two-dimensional or stereo-imaging technology. Vortex iso-surface topographies show the spatio-temporal signature of aerodynamic force generation manifest in the wake of locusts, and expose the extent to which animal wakes can deform, potentially leading to unreliable calculations of lift and thrust when using conventional diagnostic methods. We discuss implications for experimental design and analysis as volumetric flow imaging becomes more widespread.     

Occurrence and propagation of delamination during the machining of carbon fibre reinforced plastics (CFRPs) - An experimental study

The machining of carbon fibre reinforced plastics (CFRPs) is often accompanied by delamination of the top layers of the machined edges. Such damage necessitates time-consuming and costly post-machining and in some cases leads to rejection of components. The work described in this paper systematically investigates the occurrence of delamination of the top layers during the machining of CFRP tape, with the focus being on the process of contour milling. The occurrence and propagation of delamination were studied by milling slots in unidirectional CFRP specimens having different fibre orientations and mainly analysing the slot tip. This allowed the key mechanisms to be clarified. The results show that delamination is highly dependent on the fibre orientation and the tool sharpness. The experiments allow derivation of a novel system for describing the occurrence and propagation of delamination during milling. Furthermore, the principles also apply for drilling. The results allow customisation of the machining procedure to reduce and in some cases totally avoid delamination, leading to a significant increase in the quality of components.     

Scheduling flexible maintenance activities subject to job-dependent machine deterioration

This paper considers single machine scheduling that integrates machine deterioration. The current maintenance state of the machine is determined by a maintenance level which drops by a certain, possibly job-dependent, amount while jobs are processed. A maintenance level of less than zero is associated with the machine??s breakdown and is therefore forbidden. Consequently, maintenance activities that raise the maintenance level again may become necessary and have to be scheduled additionally. In what follows, two general types of maintenance activities are distinguished. In the full maintenance case, maintenance activities are always executed until the machine has reached the maximum maintenance level. In contrast to this, the schedule in the partial maintenance case has to additionally determine the duration of maintenance activities. By combining both cases with regular objective functions such as minimization of maximum tardiness, minimization of the sum of completion times, or minimization of the number of tardy jobs, we obtain a new set of specific single-stage scheduling problems. Besides motivating and introducing these problems, we shall also analyze the computational complexity of general and specific cases.