@article{GhahremaniGieseVogel2020,
  author    = {Ghahremani, Sona and Giese, Holger and Vogel, Thomas},
  title     = {Improving scalability and reward of utility-driven self-healing for large dynamic architectures},
  series = {ACM transactions on autonomous and adaptive systems},
  volume    = {14},
  journal   = {ACM transactions on autonomous and adaptive systems},
  number    = {3},
  publisher = {Association for Computing Machinery},
  address   = {New York},
  issn      = {1556-4665},
  doi       = {10.1145/3380965},
  pages     = {41},
  year      = {2020},
  abstract  = {Self-adaptation can be realized in various ways. Rule-based approaches prescribe the adaptation to be executed if the system or environment satisfies certain conditions. They result in scalable solutions but often with merely satisfying adaptation decisions. In contrast, utility-driven approaches determine optimal decisions by using an often costly optimization, which typically does not scale for large problems. We propose a rule-based and utility-driven adaptation scheme that achieves the benefits of both directions such that the adaptation decisions are optimal, whereas the computation scales by avoiding an expensive optimization. We use this adaptation scheme for architecture-based self-healing of large software systems. For this purpose, we define the utility for large dynamic architectures of such systems based on patterns that define issues the self-healing must address. Moreover, we use pattern-based adaptation rules to resolve these issues. Using a pattern-based scheme to define the utility and adaptation rules allows us to compute the impact of each rule application on the overall utility and to realize an incremental and efficient utility-driven self-healing. In addition to formally analyzing the computational effort and optimality of the proposed scheme, we thoroughly demonstrate its scalability and optimality in terms of reward in comparative experiments with a static rule-based approach as a baseline and a utility-driven approach using a constraint solver. These experiments are based on different failure profiles derived from real-world failure logs. We also investigate the impact of different failure profile characteristics on the scalability and reward to evaluate the robustness of the different approaches.},
  language  = {en}
}
@article{GhahremaniGiese2020,
  author    = {Ghahremani, Sona and Giese, Holger},
  title     = {Evaluation of self-healing systems},
  series = {Computers},
  volume    = {9},
  journal   = {Computers},
  number    = {1},
  publisher = {MDPI},
  address   = {Basel},
  issn      = {2073-431X},
  doi       = {10.3390/computers9010016},
  pages     = {32},
  year      = {2020},
  abstract  = {Evaluating the performance of self-adaptive systems is challenging due to their interactions with often highly dynamic environments. In the specific case of self-healing systems, the performance evaluations of self-healing approaches and their parameter tuning rely on the considered characteristics of failure occurrences and the resulting interactions with the self-healing actions. In this paper, we first study the state-of-the-art for evaluating the performances of self-healing systems by means of a systematic literature review. We provide a classification of different input types for such systems and analyse the limitations of each input type. A main finding is that the employed inputs are often not sophisticated regarding the considered characteristics for failure occurrences. To further study the impact of the identified limitations, we present experiments demonstrating that wrong assumptions regarding the characteristics of the failure occurrences can result in large performance prediction errors, disadvantageous design-time decisions concerning the selection of alternative self-healing approaches, and disadvantageous deployment-time decisions concerning parameter tuning. Furthermore, the experiments indicate that employing multiple alternative input characteristics can help with reducing the risk of premature disadvantageous design-time decisions.},
  language  = {en}
}
@article{FarhanRudolphNoecheletal.2018,
  author    = {Farhan, Muhammad and Rudolph, Tobias and N{\"o}chel, Ulrich and Kratz, Karl and Lendlein, Andreas},
  title     = {Extractable Free Polymer Chains Enhance Actuation Performance of Crystallizable Poly(epsilon-caprolactone) Networks and Enable Self-Healing},
  series = {Polymers},
  volume    = {10},
  journal   = {Polymers},
  number    = {3},
  publisher = {MDPI},
  address   = {Basel},
  issn      = {2073-4360},
  doi       = {10.3390/polym10030255},
  pages     = {15},
  year      = {2018},
  abstract  = {Crosslinking of thermoplastics is a versatile method to create crystallizable polymer networks, which are of high interest for shape-memory actuators. Here, crosslinked poly(epsilon-caprolactone) thermosets (cPCLs) were prepared from linear starting material, whereby the amount of extractable polymer was varied. Fractions of 5-60 wt \% of non-crosslinked polymer chains, which freely interpenetrate the crosslinked network, were achieved leading to differences in the resulting phase of the bulk material. This can be described as "sponge-like" with open or closed compartments depending on the amount of interpenetrating polymer. The crosslinking density and the average network chain length remained in a similar range for all network structures, while the theoretical accessible volume for reptation of the free polymer content is affected. This feature could influence or introduce new functions into the material created by thermomechanical treatment. The effect of interpenetrating PCL in cPCLs on the reversible actuation was analyzed by cyclic, uniaxial tensile tests. Here, high reversible strains of up to Delta epsilon = 24\% showed the enhanced actuation performance of networks with a non-crosslinked PCL content of 30 wt \% resulting from the crystal formation in the phase of the non-crosslinked PCL and co-crystallization with network structures. Additional functionalities are reprogrammability and self-healing capabilities for networks with high contents of extractable polymer enabling reusability and providing durable actuator materials.},
  language  = {en}
}
@article{WeisHessKircheretal.2019,
  author    = {Weis, Philipp and Hess, Andreas and Kircher, Gunnar and Huang, Shilin and Auernhammer, G{\"u}nter K. and Koynov, Kaloian and Butt, Hans-J{\"u}rgen and Wu, Si},
  title     = {Effects of Spacers on Photoinduced Reversible Solid-to-Liquid Transitions of Azobenzene-Containing Polymers},
  series = {Chemistry - a European journal},
  volume    = {25},
  journal   = {Chemistry - a European journal},
  number    = {46},
  publisher = {Wiley-VCH},
  address   = {Weinheim},
  issn      = {0947-6539},
  doi       = {10.1002/chem.201902273},
  pages     = {10946 -- 10953},
  year      = {2019},
  abstract  = {Photoisomerization in some azobenzene-containing polymers (azopolymers) results in reversible solid-to-liquid transitions because trans- and cis-azopolymers have different glass transition temperatures. This property enables photoinduced healing and processing of azopolymers with high spatiotemporal resolution. However, a general lack of knowledge about the influence of the polymer structure on photoinduced reversible solid-to-liquid transitions hinders the design of such novel polymers. Herein, the synthesis and photoresponsive behavior of new azopolymers with different lengths of spacers between the polymer backbone and the azobenzene group on the side chain are reported. Azopolymers with no and 20 methylene spacers did not show photoinduced solid-to-liquid transitions. Azopolymers with 6 or 12 methylene spacers showed photoinduced solid-to-liquid transitions. This study demonstrates that spacers are essential for azopolymers with photoinduced reversible solid-to-liquid transitions, and thus, gives an insight into how to design azopolymers for photoinduced healing and processing.},
  language  = {en}
}