Predicting water transport in multilayer coatings

Water transport in polymer coatings is a key process in their failure. Mostly, such systems are composed of multiple layers to meet the required specifications. Understanding water transport requires a model that relates the kinetics with the properties of the layers. In this article a theoretical model for water transport in two-layered coatings is formulated and verified. The model considers systems consisting of a hydrophobic top coat and a hydrophilic base coat. It describes the process on the basis of the top coat permeability and the base coat sorption isotherm, which define the timescale and the driving force of transport. The systems of interest had a base coat sorption isotherm, which indicated that sorption is a process of clustering of water. The non-linear isotherm shape resulted a timescale for uptake and drying of days and hours, respectively. The model is verified with NMR imaging of water transport and gravimetry. Practically, the results mean that it is sufficient to measure the top coat permeability and the base coat sorption isotherm to understand water transport kinetics in such systems.     

Practical Collisions for EnRUPT

The EnRUPT hash functions were proposed by O??Neil, Nohl and Henzen as candidates for the SHA-3 competition, organised by NIST. The proposal contains seven concrete hash functions, each with a different digest length. We present a practical collision attack on each of these seven EnRUPT variants. The time complexity of our attack varies from 2³⁶ to 2⁴⁰ round computations, depending on the EnRUPT variant, and the memory requirements are negligible. We demonstrate that our attack is practical by giving an actual collision example for EnRUPT-256.     

The helix approach: Using dynamic individual pitch control to enhance wake mixing in wind farms

Wind farm control using dynamic concepts is a research topic that is receiving an increasing amount of interest. The main concept of this approach is that dynamic variations of the wind turbine control settings lead to higher wake turbulence, and subsequently faster wake recovery due to increased mixing. As a result, downstream turbines experience higher wind speeds, thus increasing their energy capture. In dynamic induction control (DIC), the magnitude of the thrust force of an upstream turbine is varied. Although very effective, this approach also leads to increased power and thrust variations, negatively impacting energy quality and fatigue loading. In this paper, a novel approach for the dynamic control of wind turbines in a wind farm is proposed: using individual pitch control, the fixed‐frame tilt and yaw moments on the turbine are varied, thus dynamically manipulating the wake. This strategy is named the helix approach because the resulting wake has a helical shape. Large eddy simulations of a two‐turbine wind farm show that this approach leads to enhanced wake mixing with minimal power and thrust variations.     

An enhanced fast mode decision model for spatial enhancement layers in scalable video coding

Recently, the H.264/AVC standard has been extended to incorporate Scalable Video Coding (SVC). SVC offers the advantage of scalable (layered) coding, but has the disadvantage of a highly increased computational complexity at the encoder side when dealing with spatial scalability. To restrict the increase in required processing power, fast mode decision models for spatial enhancement layers have been proposed in literature. We propose a novel generic fast mode decision model for spatial enhancement layers for both P and B frames based on both the quantization of the enhancement layer and the correlation between the macroblock type in the enhancement layer and the co-located macroblock in the reference layer. In this paper, an evaluation of the proposed model and comparison with a state-of-the-art model is given. Results show that the proposed technique performs exceptionally well for spatial scalability. For both dyadic and non-dyadic spatial scalability, we achieve an average time saving of 75%, while only a slight bit rate increase of 2.23% and a minor PSNR decrease of 0.46 dB are measured. Compared with state of the art techniques, we further halve the complexity while having comparable rate-distortion results.     

Innovation Spaces: Towards a Framework for Understanding the Role of the Physical Environment in Innovation

Firms are paying increasing attention to the physical environments in which creative and innovative activities take place. These environments reflect the firm's strategic intentions towards innovation and provide a physical embodiment of their desired modes of working. To date, this new phenomenon has received little academic attention. Based on both literature and also the authors' combined experiences through observing firms in Europe, this paper proposes a simple framework to aid practitioners and academics to better understand the design, role and goals of such spaces.     

Analysis and optimal individual pitch control decoupling by inclusion of an azimuth offset in the multiblade coordinate transformation

With the trend of increasing wind turbine rotor diameters, the mitigation of blade fatigue loadings is of special interest to extend the turbine lifetime. Fatigue load reductions can be partly accomplished using individual pitch control (IPC) facilitated by the so‐called multiblade coordinate (MBC) transformation. This operation transforms and decouples the blade load signals in a yaw‐axis and tilt‐axis. However, in practical scenarios, the resulting transformed system still shows coupling between the axes, posing a need for more advanced multiple input multiple output (MIMO) control architectures. This paper presents a novel analysis and design framework for decoupling of the nonrotating axes by the inclusion of an azimuth offset in the reverse MBC transformation, enabling the application of simple single‐input single‐output (SISO) controllers. A thorough analysis is given by including the azimuth offset in a frequency‐domain representation. The result is evaluated on simplified blade models, as well as linearizations obtained from the NREL 5–MW reference wind turbine. A sensitivity and decoupling assessment justify the application of decentralized SISO control loops for IPC. Furthermore, closed‐loop high‐fidelity simulations show beneficial effects on pitch actuation and blade fatigue load reductions.     

An integrated assessment of climate change,air pollution,and energy security policy

This article presents an integrated assessment of climate change, air pollution, and energy security policy. Basis of our analysis is the MERGE model, designed to study the interaction between the global economy, energy use, and the impacts of climate change. For our purposes we expanded MERGE with expressions that quantify damages incurred to regional economies as a result of air pollution and lack of energy security. One of the main findings of our cost–benefit analysis is that energy security policy alone does not decrease the use of oil: global oil consumption is only delayed by several decades and oil reserves are still practically depleted before the end of the 21st century. If, on the other hand, energy security policy is integrated with optimal climate change and air pollution policy, the world’s oil reserves will not be depleted, at least not before our modeling horizon well into the 22nd century: total cumulative demand for oil decreases by about 24%. More generally, we demonstrate that there are multiple other benefits of combining climate change, air pollution, and energy security policies and exploiting the possible synergies between them. These benefits can be large: for Europe the achievable CO₂ emission abatement and oil consumption reduction levels are significantly deeper for integrated policy than when a strategy is adopted in which one of the three policies is omitted. Integrated optimal energy policy can reduce the number of premature deaths from air pollution by about 14,000 annually in Europe and over 3 million per year globally, by lowering the chronic exposure to ambient particulate matter. Only the optimal strategy combining the three types of energy policy can constrain the global average atmospheric temperature increase to a limit of 3 °C with respect to the pre-industrial level.     

Turbulent flow in the near field of a round impinging jet

This paper reports on detailed measurements of the turbulent flow in the stagnation region of a single impinging jet issuing from a round pipe with diameter D and a length of 76D. The distance between the pipe exit and the flat impingement plate is 2D, and the Reynolds number (based on the bulk velocity and pipe diameter) is 2.3 × 10⁴. Mean velocity components and Reynolds stresses were determined by using a two-component LDA. A modified one-component LDA was used to perform near-wall measurements with minimum wall distances of approximately 40 μm. PIV measurements were taken in a small field of view (approximately 4 × 5 mm²) to study instantaneous reversals in the near wall region.