1. The numerical analysis of flame stability in case of premixed hydrogen-air combustionMarc Jaeger, Matjaž Hriberšek, Niko Samec, Yang Guo, Xuebin Wang, Filip Kokalj, 2025, original scientific article Abstract: This study addresses the urgent need for decarbonization of heating sector, focusing on the potential of hydrogen-air combustion in gas condensing boilers. In the field of gas condensing boilers, groups of holes or slits can be used in perforated burner surfaces, providing a possible solution to the challenge of hydrogen air combustion. Real burners are always adjacent to an area with non-existent combustion, which can lead to a disturbed flame pattern. For this reason, a comparison between single-slit and multi-slit perforated flame holders with a significantly reduced structure temperature with a hydrogen-air premix is carried out as part of this study. Using Ansys Fluent, a 2D simulation approach is employed to analyze laminar flame stability behind a perforated flame holder. Inlet conditions consider fully premixed and homogenous distributed mixtures as well as nonhomogeneous premixed mixtures, with variations in pressure, velocity, and mixing degree. The model examines various slit-burner configurations and flashback behaviors based on an actual geometric shape used in a gas heating device. It has been found that with finite multi-slit burners, the bulk flow rates at the critical flashback point are 30–50% higher compared to infinitely symmetrical burners. A further deterioration of 32% is to be expected due to real mixture quality fluctuations and inhomogeneous inflow conditions. Finally, the findings demonstrate the model’s potential for designing efficient surface-stabilized burners and lay the groundwork for future 3D simulations in the pursuit of sustainable heating solutions.
Keywords: hydrogen combustion, flashback, flame stability, perforated flame holder, gas condensing boiler
Published in DKUM: 19.05.2025; Views: 0; Downloads: 3
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2. Hybrid model for motorway EV fast-charging demand analysis based on traffic volumeBojan Rupnik, Yuhong Wang, Tomaž Kramberger, 2025, original scientific article Abstract: The expected growth of electric vehicle (EV) usage will not only increase the energy demand but also bring the requirement to provide the necessary electrical infrastructure to handle the load. While charging infrastructure is becoming increasingly present in urban areas, special attention is required for transit traffic, not just for passengers but also for freight transport. Differences in the nature of battery charging compared to that of classical refueling require careful planning in order to provide a resilient electrical infrastructure that will supply enough energy at critical locations during peak hours. This paper presents a hybrid simulation model for analyzing fast-charging demand based on traffic flow, projected EV adoption, battery characteristics, and environmental conditions. The model integrates a probabilistic model for evaluating the charging requirements based on traffic flows with a discrete-event simulation (DES) framework to analyze charger utilization, waiting queues, and energy demand. The presented case of traffic flow on Slovenian motorways explored the expected power demands at various seasonal traffic intensities. The findings provide valuable insight for planning the charging infrastructure, the electrical grid, and also the layout by anticipating the number of vehicles seeking charging services. The modular design of the model allowed replacing key parameters with different traffic projections, supporting a robust scenario analysis and adaptive infrastructure planning. Replacing the parameters with real-time data opens the path for integration into a digital twin framework of individual EV charging hubs, providing the basis for development of an EV charging hub network digital twin.
Keywords: electric vehicles, EV charging, traffic flow, EV charging hub
Published in DKUM: 11.04.2025; Views: 0; Downloads: 2
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3. Local and global stimuli in reinforcement learningDanyang Jia, Hao Guo, Zhao Song, Lei Shi, Xinyang Deng, Matjaž Perc, Zhen Wang, 2021, original scientific article Abstract: In efforts to resolve social dilemmas, reinforcement learning is an alternative to imitation and exploration in evolutionary game theory. While imitation and exploration rely on the performance of neighbors, in reinforcement learning individuals alter their strategies based on their own performance in the past. For example, according to the Bush-Mosteller model of reinforcement learning, an individual's strategy choice is driven by whether the received payoff satisfies a preset aspiration or not. Stimuli also play a key role in reinforcement learning in that they can determine whether a strategy should be kept or not. Here we use the Monte Carlo method to study pattern formation and phase transitions towards cooperation in social dilemmas that are driven by reinforcement learning. We distinguish local and global players according to the source of the stimulus they experience. While global players receive their stimuli from the whole neighborhood, local players focus solely on individual performance. We show that global players play a decisive role in ensuring cooperation, while local players fail in this regard, although both types of players show properties of "moody cooperators". In particular, global players evoke stronger conditional cooperation in their neighborhoods based on direct reciprocity, which is rooted in the emerging spatial patterns and stronger interfaces around cooperative clusters.
Keywords: evolutionary game theory, cooperation, learning, social physics
Published in DKUM: 03.03.2025; Views: 0; Downloads: 1
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4. Evolutionary dynamics of any multiplayer game on regular graphsChaoqian Wang, Matjaž Perc, Attila Szolnoki, 2024, original scientific article Abstract: Multiplayer games on graphs are at the heart of theoretical descriptions of key evolutionary processes that govern vital social and natural systems. However, a comprehensive theoretical framework for solving multiplayer games with an arbitrary number of strategies on graphs is still missing. Here, we solve this by drawing an analogy with the Balls-and-Boxes problem, based on which we show that the local configuration of multiplayer games on graphs is equivalent to distributing k identical co-players among n distinct strategies. We use this to derive the replicator equation for any n-strategy multiplayer game under weak selection, which can be solved in polynomial time. As an example, we revisit the second-order free-riding problem, where costly punishment cannot truly resolve social dilemmas in a well-mixed population. Yet, in structured populations, we derive an accurate threshold for the punishment strength, beyond which punishment can either lead to the extinction of defection or transform
the system into a rock-paper-scissors-like cycle. The analytical solution also qualitatively agrees with the phase diagrams that were previously obtained for non-marginal selection strengths. Our framework thus allows an exploration of any multi-strategy multiplayer game on regular graphs.
Keywords: evolutionary game theory, cooperation, network, social physics
Published in DKUM: 26.02.2025; Views: 0; Downloads: 7
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5. Communicating sentiment and outlook reverses inaction against collective risksZhen Wang, Marko Jusup, Hao Guo, Lei Shi, Sunčana Geček, Madhur Anand, Matjaž Perc, Chris T. Bauch, Jürgen Kurths, Stefano Boccaletti, Hans-Joachim Schellnhuber, 2020, original scientific article Abstract: Collective risks permeate society, triggering social dilemmas in which working toward a common goal is impeded by selfish interests. One such dilemma is mitigating runaway climate change. To study the social aspects of climate-change mitigation, we organized an experimental game and asked volunteer groups of three different sizes to invest toward a common mitigation goal. If investments reached a preset target, volunteers would avoid all consequences and convert their remaining capital into monetary payouts. In the opposite case, however, volunteers would lose all their capital with 50% probability. The dilemma was, therefore, whether to invest one's own capital or wait for others to step in. We find that communicating sentiment and outlook helps to resolve the dilemma by a fundamental shift in investment patterns. Groups in which communication is allowed invest persistently and hardly ever give up, even when their current investment deficits are substantial. The improved investment patterns are robust to group size, although larger groups are harder to coordinate, as evidenced by their overall lower success frequencies. A clustering algorithm reveals three behavioral types and shows that communication reduces the abundance of the free-riding type. Climate-change mitigation, however, is achieved mainly by cooperator and altruist types stepping up and increasing contributions as the failure looms. Meanwhile, contributions from free riders remain flat throughout the game. This reveals that the mechanisms behind avoiding collective risks depend on an interaction between behavioral type, communication, and timing.
Keywords: social dilemma, free riding, climate change, negotiation, group size, COVID-19
Published in DKUM: 07.01.2025; Views: 0; Downloads: 4
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6. Diverse strategic identities induce dynamical states in evolutionary gamesIrene Sendiña-Nadal, Inmaculada Leyva, Matjaž Perc, David Papo, Marko Jusup, Zhen Wang, Juan A. Almendral, Pouya Manshour, Stefano Boccaletti, 2020, original scientific article Abstract: Evolutionary games provide the theoretical backbone for many aspects of our social life: from cooperation to crime, from climate inaction to imperfect vaccination and epidemic spreading, from antibiotics overuse to biodiversity preservation. An important, and so far overlooked, aspect of reality is the diverse strategic identities of individuals. While applying the same strategy to all interaction partners may be an acceptable assumption for simpler forms of life, this fails to account for the behavior of more complex living beings. For instance, we humans act differently around different people. Here we show that allowing individuals to adopt different strategies with different partners yields a very rich evolutionary dynamics, including time-dependent coexistence of cooperation and defection, systemwide shifts in the dominant strategy, and maturation in individual choices. Our results are robust to variations in network type and size, and strategy updating rules. Accounting for diverse strategic identities thus has far-reaching implications in the mathematical modeling of social games.
Keywords: cooperation, evolutionary game theory, social physics, collective dynamics, complex system
Published in DKUM: 20.11.2024; Views: 0; Downloads: 6
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7. Photonic bandgap in achiral liquid crystals - a twist on a twistDamian Pociecha, Nataša Vaupotič, Magdalena Majewska, Ewan Cruickshank, Rebecca Walker, John M. D. Storey, Corrie T. Imrie, Cheng Wang, Ewa Górecka, 2021, original scientific article Abstract: Achiral mesogenic molecules are shown to be able to spontaneously assemble into liquid crystalline smectic phases having either simple or double-helical structures. At the transition between these phases, the double-helical structure unwinds. As a consequence, in some temperature range, the pitch of the helix becomes comparable to the wavelength of visible light and the selective reflection of light in the visible range is observed. The photonic bandgap phenomenon is reported for achiral liquid crystals.
Keywords: chirality, helical structures, liquid crystals, photonic bandgap, twist–bend phases
Published in DKUM: 10.10.2024; Views: 0; Downloads: 9
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8. Evolutionary games on multilayer networks : a colloquiumZhen Wang, Lin Wang, Attila Szolnoki, Matjaž Perc, 2015, review article Abstract: Networks form the backbone of many complex systems, ranging from the Internet to human societies. Accordingly, not only is the range of our interactions limited and thus best described and modeled by networks, it is also a fact that the networks that are an integral part of such models are often interdependent or even interconnected. Networks of networks or multilayer networks are therefore a more apt description of social systems. This colloquium is devoted to evolutionary games on multilayer networks, and in particular to the evolution of cooperation as one of the main pillars of modern human societies. We first give an overview of the most significant conceptual differences between single-layer and multilayer networks, and we provide basic definitions and a classification of the most commonly used terms. Subsequently, we review fascinating and counterintuitive evolutionary outcomes that emerge due to different types of interdependencies between otherwise independent populations. The focus is on coupling through the utilities of players, through the flow of information, as well as through the popularity of different strategies on different network layers. The colloquium highlights the importance of pattern formation and collective behavior for the promotion of cooperation under adverse conditions, as well as the synergies between network science and evolutionary game theory.
Keywords: kooperacija, sociološke mreže, evolucijske igre, kolektivni pojav, samo-organizacija, fazni prehodi, recipročnost, fizika socioloških sistemov, cooperation, social networks, evolutionary games, collective phenomena, self-organization, phase transitions, reciprocity, physics of social systems
Published in DKUM: 17.09.2024; Views: 0; Downloads: 2
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9. Precision magnetometry exploiting excited state quantum phase transitionsQian Wang, Ugo Marzolino, 2024, original scientific article Abstract: Critical behaviour in phase transitions is a resource for enhanced precision metrology. The reason is that the function, known as Fisher information, is superextensive at critical points, and, at the same time, quantifies performances of metrological protocols. Therefore, preparing metrological probes at phase transitions provides enhanced precision in measuring the transition control parameter. We focus on the Lipkin-Meshkov-Glick model that exhibits excited state quantum phase transitions at different magnetic fields. Resting on the model spectral properties, we show broad peaks of the Fisher information, and propose efficient schemes for precision magnetometry. The Lipkin-Meshkov-Glick model was first introduced for superconductivity and for nuclear systems, and recently realised in several condensed matter platforms. The above metrological schemes can be also exploited to measure microscopic properties of systems able to simulate the LipkinMeshkov-Glick model.
Keywords: magnetometry, quantum phase transitions, precision, measurements
Published in DKUM: 22.08.2024; Views: 62; Downloads: 157
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10. Segregation dynamics driven by network leadersWen-Xuan Wang, Yuhao Feng, Siru Chen, Wenzhe Xu, Xinjian Zhuo, Huijia Li, Matjaž Perc, 2022, original scientific article Abstract: Network segregation - a critical problem in real-life networks - can reveal the emergence of conflicts or signal an impending collapse of the whole system. However, the strong heterogeneity of such networks and the various definitions for key nodes continue to pose challenges that limit our ability to foresee segregation and to determine the main drivers behind it. In this paper, we show that a multi-agent leader-follower consensus system can be utilized to define a new index, named leadership, to identify key leaders in real-life networks. And then, this paper explores the emergence of network segregation that is driven by these leaders based on the removal or the rewiring of the relations between different nodes in agreement with their contribution distance. We finally show that the observed leaders-driven segregation dynamics reveals the dynamics of heterogeneous attributes that critically influence network structure and its segregation. Thus, this paper provides a theoretical method to study complex social interactions and their roles in network segregation, which ultimately leads to a closed-form explanation for the emergence of imbalanced network structure from an evolutionary perspective.
Keywords: complex networks, network segregation, multi-agent leader–follower consensus system, key leaders identification, leader, segregation, social physics
Published in DKUM: 08.07.2024; Views: 122; Downloads: 24
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