480 research outputs found

    LIPIcs, Volume 251, ITCS 2023, Complete Volume

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    LIPIcs, Volume 251, ITCS 2023, Complete Volum

    Elementary fractal geometry. 3. Complex Pisot factors imply finite type

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    Self-similar sets require a separation condition to admit a nice mathematical structure. The classical open set condition (OSC) is difficult to verify. Zerner proved that there is a positive and finite Hausdorff measure for a weaker separation property which is always fulfilled for crystallographic data. Ngai and Wang gave more specific results for a finite type property (FT), and for algebraic data with a real Pisot expansion factor. We show how the algorithmic FT concept of Bandt and Mesing relates to the property of Ngai and Wang. Merits and limitations of the FT algorithm are discussed. Our main result says that FT is always true in the complex plane if the similarity mappings are given by a complex Pisot expansion factor λ\lambda and algebraic integers in the number field generated by λ.\lambda . This extends the previous results and opens the door to huge classes of separated self-similar sets, with large complexity and an appearance of natural textures. Numerous examples are provided.Comment: 28 pages, 9 figures, figures decreased to comply with size restriction for submission

    Satisfiability Modulo Finite Fields

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    We study satisfiability modulo the theory of finite fields and give a decision procedure for this theory. We implement our procedure for prime fields inside the cvc5 SMT solver. Using this theory, we con- struct SMT queries that encode translation validation for various zero knowledge proof compilers applied to Boolean computations. We evalu- ate our procedure on these benchmarks. Our experiments show that our implementation is superior to previous approaches (which encode field arithmetic using integers or bit-vectors)

    LIPIcs, Volume 261, ICALP 2023, Complete Volume

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    LIPIcs, Volume 261, ICALP 2023, Complete Volum

    Local sign stability and its implications for spectra of sparse random graphs and stability of ecosystems

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    We study the spectral properties of sparse random graphs with different topologies and type of interactions, and their implications on the stability of complex systems, with particular attention to ecosystems. Specifically, we focus on the behaviour of the leading eigenvalue in different type of random matrices (including interaction matrices and Jacobian-like matrices), relevant for the assessment of different types of dynamical stability. By comparing the results on Erdos-Renyi and Husimi graphs with sign-antisymmetric interactions or mixed sign patterns, we introduce a sufficient criterion, called strong local sign stability, for stability not to be affected by system size, as traditionally implied by the complexity-stability trade-off in conventional models of random matrices. The criterion requires sign-antisymmetric or unidirectional interactions and a local structure of the graph such that the number of cycles of finite length do not increase with the system size. Note that the last requirement is stronger than the classical local tree-like condition, which we associate to the less stringent definition of local sign stability, also defined in the paper. In addition, for strong local sign stable graphs which show stability to linear perturbations irrespectively of system size, we observe that the leading eigenvalue can undergo a transition from being real to acquiring a nonnull imaginary part, which implies a dynamical transition from nonoscillatory to oscillatory linear response to perturbations. Lastly, we ascertain the discontinuous nature of this transition.Comment: 55 pages, 17 figure

    DEFINITION OF AN ADVANCED PROCESS FOR THE PRODUCTION OF LOW ENVIRONMENTAL IMPACT CONTAINERS AS POTENTIAL ALTERNATIVE TO PLASTICS

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    For decades, petroleum-based synthetic polymers, commonly known as plastics, have become one of the most appealing materials used for a wide variety of applications. Nevertheless, currently, conventional petroleum-based plastics represent a serious problem for global pollution because remain for hundreds of years in the environment when discarded. In order to reduce dependence on fossil resources, bioplastic materials are being proposed as safer and more sustainable alternatives. Bioplastics are bio-based and/or biodegradable materials, typically derived from renewable sources. Among different resources, food waste is attracting more and more attention in the research field of bioplastics’ production. The sources of food waste include household, commercial, industrial and agricultural residues. In fact, every year, around one-third of all food resources produced for human consumption are lost or wasted. Although European Union guidelines stated that food waste should preferentially be used as animal feed, in some cases, it became illegal because of disease control concerns and other times its nutritional value is very poor. On the other hand, the production of bioplastics from food waste is a renewable, sustainable process, in which materials are fabricated from carbon neutral resources, thus aligning itself with the principles of the circular bioeconomy. However, the conversion of fruit and vegetable by-products into eco-friendly materials with mechanical and hydrodynamic performances comparable to those of fuel-based plastics still remains a challenge. In this thesis, different approaches have been investigated for the valorization of fruit and vegetable wastes to produce low environmental impact materials, as a potential alternative to plastics with application in the field of food packaging. In the first section, apple waste and tomato peel by-products have been used as fillers to fabricate starch-based biocomposites. The mechanical characterization of the samples showed their suitability for covering purposes, since a ductile and soft behaviour was exhibited. In the second section, an avocado by-product extract has been incorporated to an ethyl cellulose matrix for the production of impregnated paper with enhanced durability. Since fruit wastes can contain potential pathogens and physical and chemical contaminants which can be released when used as additive for active packaging, a preliminary untargeted metabolomic characterization of the extract was conducted by LC-ESI(-)-Q Exactive-Orbitrap- MS/MS. The lipid components detected in the extract proved to be useful additives to improve paper hydrophobicity, preventing food browning and moisture loss. In general, the addition of all tested wastes (apple waste, tomato peel and avocado by-products) has proved to be useful to increase the biodegradability of the fabricated biomaterials. Hence, the environmental benefits associated with their recovery are proposed as a driving force to expand their further use for these purposes. The upcycling of food waste through the production of value-added products is an ideal and practical end use, allowing to save huge economic and energy losses

    Universal phenomenology at critical exceptional points of nonequilibrium O(N)O(N) models

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    In thermal equilibrium the dynamics of phase transitions is largely controlled by fluctuation-dissipation relations: On the one hand, friction suppresses fluctuations, while on the other hand the thermal noise is proportional to friction constants. Out of equilibrium, this balance dissolves and one can have situations where friction vanishes due to antidamping in the presence of a finite noise level. We study a wide class of O(N)O(N) field theories where this situation is realized at a phase transition, which we identify as a critical exceptional point. In the ordered phase, antidamping induces a continuous limit cycle rotation of the order parameter with an enhanced number of 2N−32N-3 Goldstone modes. Close to the critical exceptional point, however, fluctuations diverge so strongly due to the suppression of friction that in dimensions d<4d<4 they universally either destroy a preexisting static order, or give rise to a fluctuation-induced first order transition. This is demonstrated within a non-perturbative approach based on Dyson-Schwinger equations for N=2N=2, and a generalization for arbitrary NN, which can be solved exactly in the long wavelength limit. We show that in order to realize this physics it is not necessary to drive a system far out of equilibrium: Using the peculiar protection of Goldstone modes, the transition from an xyxy magnet to a ferrimagnet is governed by an exceptional critical point once weakly perturbed away from thermal equilibrium

    Dynamic Partial Order Reduction for Checking Correctness Against Transaction Isolation Levels

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    Modern applications, such as social networking systems and e-commerce platforms are centered around using large-scale databases for storing and retrieving data. Accesses to the database are typically enclosed in transactions that allow computations on shared data to be isolated from other concurrent computations and resilient to failures. Modern databases trade isolation for performance. The weaker the isolation level is, the more behaviors a database is allowed to exhibit and it is up to the developer to ensure that their application can tolerate those behaviors. In this work, we propose stateless model checking algorithms for studying correctness of such applications that rely on dynamic partial order reduction. These algorithms work for a number of widely-used weak isolation levels, including Read Committed, Causal Consistency, Snapshot Isolation, and Serializability. We show that they are complete, sound and optimal, and run with polynomial memory consumption in all cases. We report on an implementation of these algorithms in the context of Java Pathfinder applied to a number of challenging applications drawn from the literature of distributed systems and databases.Comment: Submission to PLDI 202

    Land Surface Monitoring Based on Satellite Imagery

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    This book focuses attention on significant novel approaches developed to monitor land surface by exploiting satellite data in the infrared and visible ranges. Unlike in situ measurements, satellite data provide global coverage and higher temporal resolution, with very accurate retrievals of land parameters. This is fundamental in the study of climate change and global warming. The authors offer an overview of different methodologies to retrieve land surface parameters— evapotranspiration, emissivity contrast and water deficit indices, land subsidence, leaf area index, vegetation height, and crop coefficient—all of which play a significant role in the study of land cover, land use, monitoring of vegetation and soil water stress, as well as early warning and detection of forest ïŹres and drought
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