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    Stokes problem with the Coulomb stick-slip boundary conditions in 3D: formulations, approximation, algorithms, and experiments
    (Elsevier, 2024-02-01) Haslinger, Jaroslav; Kučera, Radek; Šátek, Václav; Motyčková, Kristina
    The paper deals with the approximation and numerical realization of the Stokes system in 3D with Coulomb's slip boundary conditions. The weak velocity-pressure formulation leads to an implicit in- equality type problem which is discretized by the P1+bubble/P1 elements. To regularize the discrete non-smooth slip term and to release the discrete impermeability condition the duality approach is used. For numerical realization of the resulting saddle-point problem two strategies are proposed, namely i) its fixed-point formulation solved by the method of successive approximations ii) the direct numerical solu- tion of the saddle-point problem. The semi-smooth Newton method is used to solve non-smooth equations appearing in both these approaches.
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    Comparing Variable Handling Strategies in BDI Agents: Experimental Study
    (SciTePress - Science and Technology Publications, 2024-02-04) Vídeňský, František; Zbořil, František; Beran, Jan; Kočí, Radek; Zbořil, František
    BDI (Belief-Desire-Intention) agents represent a paradigm in artificial intelligence, demonstrating proficiency in reasoning, planning, and decision-making. They offer a versatile framework to construct intelligent agents capable of reasoning about their beliefs, desires, and intentions. Our research focuses on AgentSpeak(L), a popular BDI language, and its interpreter using late variable bindings. Unlike traditional interpreters, it defers substitution selection until execution, enhancing rationality by preventing premature, erroneous selections. To validate our approach, we conducted experiments in a virtual collectable card marketplace. We implemented a system that can use both late and early variable binding strategies, comparing their performance. In shared and independent experiments, the late bindings strategy outperformed the early bindings strategy, although overhead costs were observed. We also conduct a brief discussion of the situations in which it is appropriate to use late bindings given the structure of the declared plans.
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    Z3-Noodler: An Automata-based String Solver
    (Springer Verlag, 2024-04-04) Chen, Yu-Fang; Chocholatý, David; Havlena, Vojtěch; Holík, Lukáš; Lengál, Ondřej; Síč, Juraj
    Z3-Noodler is a fork of Z3 that replaces its string theory solver with a custom solver implementing the recently introduced stabilization-based algorithm for solving word equations with regular constraints. An extensive experimental evaluation shows that Z3-Noodler is a fully-fledged solver that can compete with state-of-the-art solvers, surpassing them by far on many benchmarks. Moreover, it is often complementary to other solvers, making it a suitable choice as a candidate to a solver portfolio.
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    Security Implications of Deepfakes in Face Authentication
    (Association for Computing Machinery, 2024-04-08) Šalko, Milan; Firc, Anton; Malinka, Kamil
    Deepfakes are media generated by deep learning and are nearly indistinguishable from real content to humans. Deepfakes have seen a significant surge in popularity in recent years. There have been numerous papers discussing their effectiveness in deceiving people. What's equally, if not more concerning, is the potential vulnerability of facial and voice recognition systems to deepfakes. The misuse of deepfakes to spoof automated facial recognition systems can threaten various aspects of our lives, including financial security and access to secure locations. This issue remains largely unexplored. Thus, this paper investigates the technical feasibility of a spoofing attack on facial recognition. Firstly, we perform a threat analysis to understand what facial recognition use cases allow the execution of deepfake spoofing attacks. Based on this analysis, we define the attacker model for these attacks on facial recognition systems. Then, we demonstrate the ability of deepfakes to spoof two commercial facial recognition systems. Finally, we discuss possible means to prevent such spoofing attacks.
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    Mata: A Fast and Simple Finite Automata Library
    (Springer Verlag, 2024-04-04) Chocholatý, David; Fiedor, Tomáš; Havlena, Vojtěch; Holík, Lukáš; Hruška, Martin; Lengál, Ondřej; Síč, Juraj
    Mata is a well-engineered automata library written in C++ that offers a unique combination of speed and simplicity. It is meant to serve in applications such as string constraint solving and reasoning about regular expressions, and as a reference implementation of automata algorithms. Besides basic algorithms for (non)deterministic automata, it implements a fast simulation reduction and antichain-based language inclusion checking. The simplicity allows a straightforward access to the low-level structures, making it relatively easy to extend and modify. Besides the C++ API, the library also implements a Python binding. The library comes with a large benchmark of automata problems collected from relevant applications such as string constraint solving, regular model checking, and reasoning about regular expressions. We show that Mata is on this benchmark significantly faster than all libraries from a wide range of automata libraries we collected. Its usefulness in string constraint solving is demonstrated by the string solver Z3-Noodler, which is based on Mata and outperforms the state of the art in string constraint solving on many standard benchmarks.