An implicit finite wear contact formulation based on dual mortar methods

Finite deformation contact problems with frictional effects and finite shape changes due to wear are investigated. To capture the finite shape changes, a third configuration besides the well‐known reference and spatial configurations is introduced, which represents the time‐dependent worn state. Consistent interconnections between these states are realized by an arbitrary Lagrangean–Eulerian formulation. The newly developed partitioned and fully implicit algorithm is based on a Lagrangean step and a shape evolution step. Within the Lagrangean step, contact constraints as well as the wear equations are weakly enforced following the well‐established mortar framework. Additional unknowns due to the employed Lagrange multiplier method for contact constraint enforcement and due to wear itself are eliminated by condensation procedures based on the concept of biorthogonality and the so‐called dual shape functions. Several numerical examples in both 2D and 3D are provided to demonstrate the performance and accuracy of the proposed numerical algorithm. Copyright © 2016 John Wiley & Sons, Ltd.     

Process modelling of an alkaline water electrolyzer

In this paper a model for the prediction of the product gas purity in alkaline water electrolysis is proposed. For the estimation of the exhaust gas compositions the operating conditions, such as current density, electrolyte flow rate, concentration and temperature as well as process management possibilities are considered. The development of the model relies on a classical process engineering approach and depicts the electrolysis cell through coupled continuously stirred-tank reactors. Furthermore, the mass transport phenomena between the phases are considered through the application of Reynolds and Sherwood correlations. Finally, the validation of the model is performed through experiments, which are carried out in a lab-scale electrolyzer with a 150 cm² zero-gap cell and KOH electrolyte at atmospheric pressure. This investigation reveals that gas purity in alkaline water electrolysis is mainly affected by mixing the anodic and cathodic electrolyte cycles, which transport dissolved electrolysis products into the opposite half cell compartments. However, this transport mechanism can be significantly reduced by adjustment of the operating conditions of the electrolyzer.     

Natural Killer Cells—An Epigenetic Perspective of Development and Regulation

Based on their ability to recognize and eliminate various endo- and exogenous pathogens as well as pathological alterations, Natural Killer (NK) cells represent an important part of the cellular innate immune system. Although the knowledge about their function is growing, little is known about their development and regulation on the molecular level. Research of the past decade suggests that modifications of the chromatin, which do not affect the base sequence of the DNA, also known as epigenetic alterations, are strongly involved in these processes. Here, the impact of epigenetic modifications on the development as well as the expression of important activating and inhibiting NK-cell receptors and their effector function is reviewed. Furthermore, external stimuli such as physical activity and their influence on the epigenetic level are discussed.     

Evolutionary mechanics: new engineering principles for the emergence of flexibility in a dynamic and uncertain world

Engineered systems are designed to deftly operate under predetermined conditions yet are notoriously fragile when unexpected perturbations arise. In contrast, biological systems operate in a highly flexible manner; learn quickly adequate responses to novel conditions, and evolve new routines and traits to remain competitive under persistent environmental change. A recent theory on the origins of biological flexibility has proposed that degeneracy-the existence of multi-functional components with partially overlapping functions-is a primary determinant of the robustness and adaptability found in evolved systems. While degeneracy's contribution to biological flexibility is well documented, there has been little investigation of degeneracy design principles for achieving flexibility in systems engineering. Actually, the conditions that can lead to degeneracy are routinely eliminated in engineering design. With the planning of transportation vehicle fleets taken as a case study, this article reports evidence that degeneracy improves the robustness and adaptability of a simulated fleet towards unpredicted changes in task requirements without incurring costs to fleet efficiency. We find that degeneracy supports faster rates of design adaptation and ultimately leads to better fleet designs. In investigating the limitations of degeneracy as a design principle, we consider decision-making difficulties that arise from degeneracy's influence on fleet complexity. While global decision-making becomes more challenging, we also find degeneracy accommodates rapid distributed decision-making leading to (near-optimal) robust system performance. Given the range of conditions where favorable short-term and long-term performance outcomes are observed, we propose that degeneracy may fundamentally alter the propensity for adaptation and is useful within different engineering and planning contexts.