Time-Optimal Coordination of Flexible Manufacturing Systems Using Deterministic Finite Automata and Mixed Integer Linear Programming

Automation and flexibility are often mentioned as key concepts in modern production industry. To increase the level of flexibility, deterministic finite automata (DFA) can be used to model, specify and verify the production systems. Often, it is also desirable to optimize some production criteria, such as for example the cycle time of a manufacturing cell. In this paper, a method for automatic conversion from DFA to a mixed integer linear programming (MILP) formulation is first presented. This conversion is developed for a number of DFA structures that have shown to be useful in practical applications. Special attention is paid to reducing the search region explored by the MILP solver. Second, a conversion from the MILP solution to a DFA supervisor is described. This allows to combine the advantages of DFA modeling with the efficiency of MILP and supervisory control theory to automatically generate time-optimal, collision-free and non-blocking working schedules for flexible manufacturing systems.

A Taxonomy and Survey of Dynamic Graph Visualization

Dynamic graph visualization focuses on the challenge of representing the evolution of relationships between entities in readable, scalable and effective diagrams. This work surveys the growing number of approaches in this discipline. We derive a hierarchical taxonomy of techniques by systematically categorizing and tagging publications. While static graph visualizations are often divided into node‐link and matrix representations, we identify the representation of time as the major distinguishing feature for dynamic graph visualizations: either graphs are represented as animated diagrams or as static charts based on a timeline. Evaluations of animated approaches focus on dynamic stability for preserving the viewer's mental map or, in general, compare animated diagrams to timeline‐based ones. A bibliographic analysis provides insights into the organization and development of the field and its community. Finally, we identify and discuss challenges for future research. We also provide feedback from experts, collected with a questionnaire, which gives a broad perspective of these challenges and the current state of the field.     

Cross-system user modeling and personalization on the Social Web

In order to adapt functionality to their individual users, systems need information about these users. The Social Web provides opportunities to gather user data from outside the system itself. Aggregated user data may be useful to address cold-start problems as well as sparse user profiles, but this depends on the nature of individual user profiles distributed on the Social Web. For example, does it make sense to re-use Flickr profiles to recommend bookmarks in Delicious? In this article, we study distributed form-based and tag-based user profiles, based on a large dataset aggregated from the Social Web. We analyze the completeness, consistency and replication of form-based profiles, which users explicitly create by filling out forms at Social Web systems such as Twitter, Facebook and LinkedIn. We also investigate tag-based profiles, which result from social tagging activities in systems such as Flickr, Delicious and StumbleUpon: to what extent do tag-based profiles overlap between different systems, what are the benefits of aggregating tag-based profiles. Based on these insights, we developed and evaluated the performance of several cross-system user modeling strategies in the context of recommender systems. The evaluation results show that the proposed methods solve the cold-start problem and improve recommendation quality significantly, even beyond the cold-start.     

Is there a gender-based fragmentation of communication science? An investigation of the reasons for the apparent gender homophily in citations

Multiple studies report that male scholars cite publications of male authors more often than their female colleagues do—and vice versa. This gender homophily in citations points to a fragmentation of science along gender boundaries. However, it is not yet clear whether it is actually (perceived) gender characteristics or structural conditions related to gender that are causing the heightened citation frequency of same-sex authors. A bibliometric study on the two leading German communication science journals Publizistik and Medien & Kommunikationswissenschaft was employed to further analyze the causes of the phenomenon. As scholars tend to primarily cite sources from their own area of research, differences among male and female scholars regarding their engagement in certain research fields become relevant. It was thus hypothesized that the research subject might mediate the relationship between the citing and cited authors’ genders. A first analysis based on n = 917 papers published in the period from 1970 to 2009 confirmed the expected gender-differences regarding research-activity in certain fields. Subsequently, structural equation modeling was employed to test the suggested mediation model. Results show the expected mediation to be a complementary one indicating that gender homophily in citations is partly due to topical boundaries. While there are alternative explanations for the remaining direct effect, it may suggest that a fragmentation of science along gender boundaries is indeed an issue that communication science must face.     

Solution Mask Liquid Lithography (SMaLL) for One‐Step,Multimaterial 3D Printing

A novel methodology for printing 3D objects with spatially resolved mechanical and chemical properties is reported. Photochromic molecules are used to control polymerization through coherent bleaching fronts, providing large depths of cure and rapid build rates without the need for moving parts. The coupling of these photoswitches with resin mixtures containing orthogonal photo‐crosslinking systems allows simultaneous and selective curing of multiple networks, providing access to 3D objects with chemically and mechanically distinct domains. The power of this approach is showcased through the one‐step fabrication of bioinspired soft joints and mechanically reinforced “brick‐and‐mortar” structures.     

Recent Advances and Perspectives on Powder-Based Halide Perovskite Film Processing

Halide perovskites have undergone an impressive development and could be used in a wide range of optoelectronic devices, where some of them are already at the edge of commercialization, e.g., perovskite solar cells. Recently, interest in perovskites in powder form has increased, as for example, they are found to exhibit high stability and allow for easy production of large quantities. Accordingly, also the topic of processing thin and thick films on the basis of perovskite powders is currently gaining momentum. Here, perovskite powder can form the basis for both, typical wet and solvent-based processing approaches, as well as for dry processes. In this Progress Report, the recent developments of halide perovskites in powder form and of film processing approaches are summarized that are based on them. The advantages and opportunities of the different processing methods are highlighted, but their individual drawbacks and limitations are also discussed. Prospects are also pointed out and possible steps necessary to unlock the full potential of powder-based processing methods for producing high quality thick and thin perovskite layers in the future are discussed.     

Bombalytics: Visualization of Competition and Collaboration Strategies of Players in a Bomb Laying Game

Competition and collaboration form complex interaction patterns between the agents and objects involved. Only by understanding these interaction patterns, we can reveal the strategies the participating parties applied. In this paper, we study such competition and collaboration behavior for a computer game. Serving as a testbed for artificial intelligence, the multiplayer bomb laying game Pommerman provides a rich source of advanced behavior of computer agents. We propose a visualization approach that shows an overview of multiple games, with a detailed timeline-based visualization for exploring the specifics of each game. Since an analyst can only fully understand the data when considering the direct and indirect interactions between agents, we suggest various visual encodings of these interactions. Based on feedback from expert users and an application example, we demonstrate that the approach helps identify central competition strategies and provides insights on collaboration.     

Link state opportunistic routing for multihop wireless networks

Wireless Networks - Enhancing the quality of service is the crucial issue of future wireless networks. In this paper, we propose a new multihop wireless routing protocol inspired by opportunistic...     

Tuning Channel Architecture of Interdigitated Organic Electrochemical Transistors for Recording the Action Potentials of Electrogenic Cells

Organic electrochemical transistors (OECTs) have emerged as versatile electrophysiological sensors due to their high transconductance, biocompatibility, and transparent channel material. High maximum transconductances are demonstrated facilitating the extracellular recording of signals from electrogenic cells. However, this requires large channel dimensions and thick polymer films. These large channel dimensions lead to low transistor densities. Here, interdigitated OECTs (iOECTs) are introduced, which feature high transconductances at small device areas. A superior device performance is achieved by systematically optimizing the electrode layout regarding channel length, number of electrode fingers and electrode width. Interestingly, the maximum transconductance (g_max) does not straightforwardly scale with the channel width‐to‐length ratio, which is different from planar OECTs. This deviation is caused by the dominating influence of the source–drain series resistance R_sd for short channel devices. Of note, there is a critical channel length (15 µm) above which the channel resistance R_ch becomes dominant and the device characteristics converge toward those of planar OECTs. Design rules for engineering the performance of iOECTs are proposed and tested by recording action potentials of cardiomyocyte‐like HL‐1 cells with high signal‐to‐noise ratios. These results demonstrate that interdigitated OECTs meet two requirements of bioelectronic applications, namely, high device performance and small channel dimensions.     

驾驭自然资源

海上风电作为便宜且可再生的能源，世界各国政府都希望能对其加以利用。然而，在海洋环境中开发风电场会面临一系列新的工程挑战。比如说，在设计海上风力涡轮机支撑结构时，支撑结构必须能够承载着大型风力涡轮机在深水环境中正常运转。在设计这种成本效益型且可靠的海上风力涡轮机大型结构时，工程仿真就成了宝贵的工具。