A Component-oriented Framework for Autonomous Agents

The design of a complex system warrants a compositional methodology, i.e., composing simple components to obtain a larger system that exhibits their collective behavior in a meaningful way. We propose an automaton-based paradigm for compositional design of such systems where an action is accompanied by one or more preferences. At run-time, these preferences provide a natural fallback mechanism for the component, while at design-time they can be used to reason about the behavior of the component in an uncertain physical world. Using structures that tell us how to compose preferences and actions, we can compose formal representations of individual components or agents to obtain a representation of the composed system. We extend Linear Temporal Logic with two unary connectives that reflect the compositional structure of the actions, and show how it can be used to diagnose undesired behavior by tracing the falsification of a specification back to one or more culpable components

Exploiting the Hierarchical Structure of Rule-Based Specifications for Decision Planning

Rule-based specifications have been very successful as a declarative approach in many domains, due to the handy yet solid foundations offered by rule-based machineries like term and graph rewriting. Realistic problems, however, call for suitable techniques to guarantee scalability. For instance, many domains exhibit a hierarchical structure that can be exploited conveniently. This is particularly evident for composition associations of models. We propose an explicit representation of such structured models and a methodology that exploits it for the description and analysis of model- and rule-based systems. The approach is presented in the framework of rewriting logic and its efficient implementation in the rewrite engine Maude and is illustrated with a case study.

Solitary magnetic perturbations at the ELM onset

Edge localised modes (ELMs) allow maintaining sufficient purity of tokamak H-mode plasmas and thus enable stationary H-mode. On the other hand in a future device ELMs may cause divertor power flux densities far in excess of tolerable material limits. The size of the energy loss per ELM is determined by saturation effects in the non-linear phase of the ELM, which at present is hardly understood. Solitary magnetic perturbations (SMPs) are identified as dominant features in the radial magnetic fluctuations below 100kHz. They are typically observed close (+-0.1ms) to the onset of pedestal erosion. SMPs are field aligned structures rotating in the electron diamagnetic drift direction with perpendicular velocities of about 10km/s. A comparison of perpendicular velocities suggests that the perturbation evoking SMPs is located at or inside the separatrix. Analysis of very pronounced examples showed that the number of peaks per toroidal turn is 1 or 2, which is clearly lower than corresponding numbers in linear stability calculations. In combination with strong peaking of the magnetic signals this results in a solitary appearance resembling modes like palm tree modes, edge snakes or outer modes. This behavior has been quantified as solitariness and correlated to main plasma parameters. SMPs may be considered as a signature of the non-linear ELM-phase originating at the separatrix or further inside. Thus they provide a handle to investigate the transition from linear to non-linear ELM phase. By comparison with data from gas puff imaging processes in the non-linear phase at or inside the separatrix and in the scrape-off-layer (SOL) can be correlated. A connection between the passing of an SMP and the onset of radial filament propagation has been found. Eventually the findings related to SMPs may contribute to a future quantitative understanding of the non-linear ELM evolution.Comment: submitted to Nuclear Fusio

Bioink properties before, during and after 3D bioprinting

Bioprinting is a process based on additive manufacturing from materials containing living cells. These materials, often referred to as bioink, are based on cytocompatible hydrogel precursor formulations, which gel in a manner compatible with different bioprinting approaches. The bioink properties before, during and after gelation are essential for its printability, comprising such features as achievable structural resolution, shape fidelity and cell survival. However, it is the final properties of the matured bioprinted tissue construct that are crucial for the end application. During tissue formation these properties are influenced by the amount of cells present in the construct, their proliferation, migration and interaction with the material. A calibrated computational framework is able to predict the tissue development and maturation and to optimize the bioprinting input parameters such as the starting material, the initial cell loading and the construct geometry. In this contribution relevant bioink properties are reviewed and discussed on the example of most popular bioprinting approaches. The effect of cells on hydrogel processing and vice versa is highlighted. Furthermore, numerical approaches were reviewed and implemented for depicting the cellular mechanics within the hydrogel as well as for prediction of mechanical properties to achieve the desired hydrogel construct considering cell density, distribution and material-cell interaction

Differential Hoare Logics and Refinement Calculi for Hybrid Systems with Isabelle/HOL

We present simple new Hoare logics and refinement calculi for hybrid systems in the style of differential dynamic logic. (Refinement) Kleene algebra with tests is used for reasoning about the program structure and generating verification conditions at this level. Lenses capture hybrid program stores in a generic algebraic way. The approach has been formalised with the Isabelle/HOL proof assistant. A number of examples explains the workflow with the resulting verification components

Experimental evidence of magnetic flux pumping in ASDEX upgrade

In high-β scenarios with on-axis co-current electron cyclotron current drive, which normally lowers q 0 below unity, the absence of sawteeth suggests the involvement of an additional current redistribution mechanism beyond neoclassical current diffusion. This is supported by imaging motional Stark effect diagnostic measurements, which indicate that q 0 remains consistently around 1. This phenomenon is observed in the presence of a 1/1 mode, indicating its potential role in the current redistribution. It is shown that the mode’s ability to modify the central current and suppress sawteeth increases with plasma pressure. These findings align with a recent theoretical model, which predicts a pressure threshold for sawtooth avoidance by a 1/1 quasi-interchange mode and where this threshold increases with the strength of inward current diffusion. Moreover, the advantages of the flux pumping scenario for future machines are highlighted.</p

Experimental evidence of magnetic flux pumping in ASDEX upgrade

In high-β scenarios with on-axis co-current electron cyclotron current drive, which normally lowers q 0 below unity, the absence of sawteeth suggests the involvement of an additional current redistribution mechanism beyond neoclassical current diffusion. This is supported by imaging motional Stark effect diagnostic measurements, which indicate that q 0 remains consistently around 1. This phenomenon is observed in the presence of a 1/1 mode, indicating its potential role in the current redistribution. It is shown that the mode’s ability to modify the central current and suppress sawteeth increases with plasma pressure. These findings align with a recent theoretical model, which predicts a pressure threshold for sawtooth avoidance by a 1/1 quasi-interchange mode and where this threshold increases with the strength of inward current diffusion. Moreover, the advantages of the flux pumping scenario for future machines are highlighted.</p

Self-similar chain conformations in polymer gels

We use molecular dynamics simulations to study the swelling of randomly end-cross-linked polymer networks in good solvent conditions. We find that the equilibrium degree of swelling saturates at Q_eq = N_e**(3/5) for mean strand lengths N_s exceeding the melt entanglement length N_e. The internal structure of the network strands in the swollen state is characterized by a new exponent nu=0.72. Our findings are in contradiction to de Gennes' c*-theorem, which predicts Q_eq proportional N_s**(4/5) and nu=0.588. We present a simple Flory argument for a self-similar structure of mutually interpenetrating network strands, which yields nu=7/10 and otherwise recovers the classical Flory-Rehner theory. In particular, Q_eq = N_e**(3/5), if N_e is used as effective strand length.Comment: 4 pages, RevTex, 3 Figure