Integrated operation of diagnostic and control systems

In fusion research the ability to generate and sustain high performance fusion plasmas gains more and more importance. Optimal combinations of magnetic shape, temperature and density profiles as well as the confinement time are identified as advanced regimes. Safe operation in such regimes will be crucial for the success of ITER and later fusion reactors. The operational space, on the other hand, is characterized by nonlinear dependencies between plasma parameters. Various MHD limits must be avoided in order to minimize the risk of a disruption.Sophisticated feedback control schemes help to tackle this challenge. But these in turn require detailed information on plasma state in time to allow proper reaction. Control system and diagnostic systems therefore must establish a symbiotic relationship to carry out such schemes. Today, all major fusion devices implement such a concept.An implementation of such a concept with sustained integration is presented using the example of ASDEX Upgrade. It covers data communication via a real-time network, synchronization mechanisms for data-driven algorithm execution as well as operational aspects and exception handling for failure detection and recovery. A modular distributed software framework offers standardized user algorithm interfaces, automated workflow procedures and the application of various computer and network hardware components. Designed with a special focus on reliability, robustness and flexibility, it is a sound base for exploring ITER-relevant plasma regimes and control strategies.     

Fretting damage in thin sheets: Analysis of an experimental configuration

A method for evaluating fretting damage in thin sheets was developed for AISI 301 stainless steel in full hard condition in contact with AISI 52100 steel and cast ANSI A356 aluminum. Samples were subjected to fretting and then were subsequently fatigue tested to determine the impact of the fretting damage on fatigue life. A finite element model of the experimental configuration was used to determine the response for the experimental conditions imposed. The values of Fatemi-Socie critical-plane fatigue damage parameter are shown to correspond to the trends in the observed residual fatigue life for contact with AISI 52100 steel.     

Salimyxins and Enhygrolides: Antibiotic,Sponge‐Related Metabolites from the Obligate Marine Myxobacterium Enhygromyxa salina

Unlike their terrestrial counterparts, marine myxobacteria are hardly investigated for their secondary metabolites. This study describes three new compounds ( 1 – 3 ), named salimyxins and enhygrolides, obtained from the obligate marine myxobacterium Enhygromyxa salina. These are the first natural products obtained from Enhygromyxa species. Their structures were elucidated by spectroscopic analysis, including NMR and CD spectroscopy. Enhygrolides are closely related to the nostoclides, which were initially isolated from a cyanobacterium of the genus Nostoc. The salimyxins, representing structurally most unusual degraded sterols, are close to identical to demethylincisterol from the sponge Homaxinella sp. Salimyxin B and enhygrolide A inhibit the growth of the Gram‐positive bacterium Arthrobacter cristallopoietes (MIC salimyxin B, 8 μg mL^?1; enhygrolide A, 4 μg mL^?1).     

Microstructure‐sensitive fatigue modelling of medical‐grade fine wire

This work presents a modelling methodology to assess the sensitivity to microstructure in high‐cycle fatigue performance of fine wires made from MP35N alloy (35Ni‐35Co‐20Cr‐10Mo in wt%) used as conductors in cardiac leads. The model consists of a microstructure generator that creates a mesh of a statistically representative microstructure, a finite element analysis using a crystal plasticity constitutive model to determine the local response behaviour of the microstructure, and a postprocesser using fatigue indicating parameters to assess the likelihood of fatigue crack initiation. The fatigue crack initiation potency for selected microstructure attributes, boundary and interface conditions, and loading profiles is determined by computing the Fatemi‐Socie fatigue indicating parameter over a physically relevant volume of scale. Case studies are used to investigate (1) the influence of nonmetallic inclusion proximity to the wire surface on fatigue potency and (2) the transition life demarcating lives primarily controlled by fatigue crack initiation versus microcrack fatigue growth.     

Transition modelling of surface flaws to through cracks

Cracks starting at surfaces will grow under fatigue loading conditions both along the surface and in the thickness directions of the component geometry. In those cases where the crack grows through the thickness, the fatigue crack may transition to a corresponding through crack geometry. While the fatigue crack growth behaviour of both the surface flaws and complete through cracks are well understood, the method for modelling the process by which they transition from one to the other is not. This paper seeks to bring greater clarity and understanding to the transition process by implementing a transition method and developing the associated codes and equations to do so based on careful consideration of boundary conditions, experimental data, and finite element simulations.     

Recellularization and Integration of Dense Extracellular Matrix by Percolation of Tissue Microparticles

Cells embedded in the extracellular matrix of tissues play a critical role in maintaining homeostasis while promoting integration and regeneration following damage or disease. Emerging engineered biomaterials utilize decellularized extracellular matrix as a tissue-specific support structure; however, many dense, structured biomaterials unfortunately demonstrate limited formability, fail to promote cell migration, and result in limited tissue repair. Here, a reinforced composite material of densely packed acellular extracellular matrix microparticles in a hydrogel, termed tissue clay, that can be molded and crosslinked to mimic native tissue architecture is developed. Hyaluronic acid-based hydrogels are utilized, amorphously packed with acellular cartilage tissue particulated to ≈125–250 microns in diameter and defined a percolation threshold of 0.57 (v/v) beyond which the compressive modulus exceeded 300 kPa. Remarkably, primary chondrocytes recellularize particles within 48 h, a process driven by chemotaxis, exhibit distributed cellularity in large engineered composites, and express genes consistent with native cartilage repair. In addition, broad utility of tissue clays through recellularization and persistence of muscle, skin, and cartilage composites in an in vivo mouse model is demonstrated. The findings suggest optimal material architectures to balance concurrent demands for large-scale mechanical properties while also supporting recellularization and integration of dense musculoskeletal and connective tissues.     

Microstructure sensitivity of fretting fatigue based on computational crystal plasticity

Three-dimensional finite element simulations are conducted to study the effects of microstructure on the fretting fatigue behavior of duplex Ti-6Al-4V. These fretting simulations involve a rigid cylindrical indenter pressed on the half space of Ti-6Al-4V with different realizations of microstructure. The deformation behaviors of the primary α and α/β lamellar phases at room temperature are described by three-dimensional crystal plasticity constitutive relations. Microstructure attributes considered in this sensitivity study include crystallographic texture, grain size, and grain size distribution. Voronoi tessellation is used to construct the three-dimensional finite element models with various grain size distributions. The plastic strain behaviors and the distribution of the average maximum plastic shear strain among grains are analyzed and contrasted. The relative susceptibility for crack formation, including effects of various microstructure features, is determined using the Fatemi-Socie parameter. The results suggest that both average grain size and especially crystallographic texture have more influence on the plastic deformation and fretting fatigue behavior than grain size distribution for the fretting condition considered.     

Der elektrische Widerstand eines Drahtgitters

Übersicht Der Aufsatz beschreibt ein Verfahren, nach dem sich der Widerstand zwischen zwei einander gegenüberliegenden Ecken eines quadratischen Gitters abhängig von der Maschenzahl berechnen läßt.Zunächst wird eine Potentialfunktion definiert, die nicht nur in den Knotenpunkten des Gitters erklärt ist, sondern in der ganzen Ebene, in der das Gitter liegt. Diese Funktion läßt sich mit der zweidimensionalen Laplace-Transformation aus den Einströmungen und den Randwerten berechnen. Die Randwerte dieser Funktion werden ermittelt. Sie gestatten, den gesuchten Widerstand zu bestimmen, so daß eine exakte Formel angegeben werden kann. Eine Abschätzung der gefundenen Formel rundet die Untersuchung ab.

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Summary The article describes a method of calculating the resistance between two diagonal corners of a square network as a function of the number of meshes.The author defines a potential function, which holds good not only in the knots of the network, but also in the whole plane in which the network lies. This function can be calculated out of the impressed current and the boundary conditions with the help of the two-dimensional Laplace transformation. The boundary conditions of this function are ascertained. They allow the determination of the resistance in question and leads to an exact formula. A numerical estimation of the exact formula concludes the problem.

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Mit 7 Textabbildungen     

A parametric cubic modelling system for general solids of composite material

A new approach to modelling solids that are anisotropic and heterogeneous is presented with applications to structures of composite material. A parametric cubic modelling system is presented for lines, surfaces, volumes, and physical data that uses construction-in-context to generate numerical data. This system automates the construction of discrete element models and can reduce input data requirements by more than an order of magnitude. A tricubic isoparametric discrete element is presented that does not require displacement derivatives to define connectivity. This element is capable of exact displacement and strain continuity over a surface while permitting strain discontinuities at heterogeneous material interfaces. The shape of an element can be any hexahedron, pentahedron, or tetrahedron and the material properties are allowed to vary over the volume. Evaluation of modelling error with respect to closed-form solutions for curved geometries indicate a single element can model up to 90-degree segments with stresses accurate to 1 per cent. Applications of the system to composite structures are presented for interlaminar edge effects and attachment stresses in a sandwich panel.