A Comprehensive Study of k-Portfolios of Recent SAT Solvers

Hard combinatorial problems such as propositional satisfiability are ubiquitous. The holy grail are solution methods that show good performance on all problem instances. However, new approaches emerge regularly, some of which are complementary to existing solvers in that they only run faster on some instances but not on many others. While portfolios, i.e., sets of solvers, have been touted as useful, putting together such portfolios also needs to be efficient. In particular, it remains an open question how well portfolios can exploit the complementarity of solvers. This paper features a comprehensive analysis of portfolios of recent SAT solvers, the ones from the SAT Competitions 2020 and 2021. We determine optimal portfolios with exact and approximate approaches and study the impact of portfolio size k on performance. We also investigate how effective off-the-shelf prediction models are for instance-specific solver recommendations. One result is that the portfolios found with an approximate approach are as good as the optimal solution in practice. We also observe that marginal returns decrease very quickly with larger k, and our prediction models do not give way to better performance beyond very small portfolio sizes

Active Learning for SAT Solver Benchmarking

Benchmarking is a crucial phase when developing algorithms. This also applies to solvers for the SAT (propositional satisfiability) problem. Benchmark selection is about choosing representative problem instances that reliably discriminate solvers based on their runtime. In this paper, we present a dynamic benchmark selection approach based on active learning. Our approach predicts the rank of a new solver among its competitors with minimum runtime and maximum rank prediction accuracy. We evaluated this approach on the Anniversary Track dataset from the 2022 SAT Competition. Our selection approach can predict the rank of a new solver after about 10 % of the time it would take to run the solver on all instances of this dataset, with a prediction accuracy of about 92 %. We also discuss the importance of instance families in the selection process. Overall, our tool provides a reliable way for solver engineers to determine a new solver’s performance efficiently

Identifizierung des orthologen Ergothionein-Transporters des Zebrafischs, Etablierung und Phänotypisierung des Knockout-Modells

Ergothionein (ET) ist ein natürliches Antioxidans, das nur von Pilzen und einigen Mykobakterien synthetisiert werden kann. Aufgrund der permanenten Ladungen ist ET nicht in der Lage ohne die Hilfe eines Transporters eine intakte Biomembran nennenswert zu passieren. Dies ist die physiologische Aufgabe des Ergothionein-Transporters (ETT, Gensymbol SLC22A4). Genetische Varianten des ETT konnten mit chronischen Entzündungskrankheiten, wie Morbus Crohn oder ulzerativer Kolitis, assoziiert werden. Des Weiteren gibt es Anzeichen dafür, dass der Transporter bzw. ET bei der Entstehung von Typ I Diabetes sowie grauem Star (Katarakt) eine Rolle spielt. Die physiologische Bedeutung von ET ist noch unklar, jedoch deuten die chemischen Eigenschaften und die hohen Konzentrationen in bestimmten Geweben, die hohem oxidativem Stress ausgesetzt sind, auf einen antioxidativen Schutz hin. Da bisherige Untersuchungen zur Funktion von ET überwiegend in vitro durchgeführt wurden, war es Ziel dieser Arbeit ein Zebrafisch-Knockout-Modell für den ETT zu etablieren. Mittels Sequenzanalyse konnten im Zebrafisch drei Kandidaten für einen orthologen ETT gefunden werden, die aufgrund der Sequenzidentität nicht eindeutig den humanen Transportern (ETT bzw. CTT, Gensymbol SLC22A5) aus der SLC22-Familie zugeordnet werden konnten. Nach der Klonierung und funktionellen Charakterisierung konnte genau ein ETT-Ortholog im Zebrafisch identifiziert werden. Die Analyse der Expression zeigte deutliche Gemeinsamkeiten zum humanen ETT und die in vivo Aktivität eines ETTs konnte im Zebrafisch mittels LC-MS gemessen werden. Um den Effekt von ET auf den Organismus zu untersuchen, wurde eine Fischlinie etabliert, die den orthologen Ergothionein-Transporter aufgrund einer retroviralen Insertion im ersten Exon nicht mehr exprimiert. Diese ettzf-/--Fische (zf: zebrafish) sind nicht mehr in der Lage ET zu akkumulieren. Die Fische zeigen einen vollständigen ET-Mangel und ermöglichen erstmals Folgen dieses Mangels in vivo zu untersuchen. Die Phänotypisierung der Fische zeigte bisher unter normalen Laborbedingungen keine Mangelerscheinungen

Assessing the availability of terrestrial biotic materials in product systems (BIRD)

Availability of abiotic resources has been a topic of concern in recent years, resulting in several approaches being published to determine their availability on country and product level. However, the availability of biotic materials has not been analyzed to this extent yet. Therefore, an approach to determine possible limitations to availability of terrestrial biotic materials over the entire supply chain is introduced. The approach considers 24 categories overall as well as associated category indicators for the five dimensions: physical, socio-economic, abiotic, social and environmental constraints. This ensures a comprehensive availability assessment of bio-based product systems. The approach is applied to a case study comparing biodiesel produced from rapeseed and soy beans. The study shows that the determination of indicator values is feasible for most categories and their interpretation leads to meaningful conclusions. Thus, the approach leads to a more comprehensive assessment of availability aspects and supports better informed decision making in industry and policy.DFG, 325093850, Open Access Publizieren 2017 - 2018 / Technische Universität Berli

Comprehensive approach for evaluating different resource types – Case study of abiotic and biotic resource use assessment methodologies

Due to steadily increasing resource demand and accompanying raising public awareness, a variety of assessment methodologies evaluating resource use and its consequences were published in the last years. Existing methodologies are typically developed considering the specific characteristics of one particular resource type and as consequence are not suitable for cross-cutting assessment of different resource types. This paper proposes an 3-step approach for combining different resource use assessment methodologies allowing for a consistent assessment of product systems using different resource types. The first steps evaluate if the considered dimensions, categories, indicators, indicator models and underlying data are consistent. When this is the case, they can be included in the combined methodology without further adjustments. Differences are identified simultaneously and addressed in the subsequent steps. Within the steps guidance is provided on how the dimensions, categories and indicators of the methodologies can be adjusted to fit in the combined methodology. In a case study the proposed approach is applied to two methodologies developed by the authors assessing abiotic (ESSENZ method) and biotic resources and raw materials (BIRD method). The ESSENZ method consists of four dimensions, which are quantified by overall 21 categories and indicators. The BIRD method takes into account five dimensions and 24 corresponding categories and indicators. As none of the considered dimension of the two methodologies match, comparison of the considered resource types as well as application in a case study is not possible. By applying the proposed approach all five dimensions and 25 of the overall 27 categories and indicators can be integrated in the combined approach for a consistent assessment of abiotic and biotic resources and raw materials. The obtained combined methodology is then applied to three shelves made out of metal, wood and plastic. It could be shown that the introduced approach provides meaningful guidance on how to combine different resource use assessment methodologies and increases the findings gained from a combined and consistent assessment.DFG,353450346, Bewertung der Inanspruchnahme biotischer und abiotischer Ressourcen im Mobilitätssektor -Entwicklung von Ökobilanz-kompatiblen Bewertungskriterien, -methoden und -konzepte

Hybrid approach for the evaluation of organizational indirect impacts (AVOID): combining product-related, process-based, and monetary-based methods

Purpose: Environmental burden caused by an organization occurs both within its boundaries and in its value chain. Organizational life cycle assessment (LCA) was proposed as a method for calculating impacts of an organization throughout its life cycle; nevertheless, companies are still lacking a universal approach to conduct inventory analysis and face challenges in data collection. This paper introduces a hybrid approach for compiling the inventory for the indirect activities on organizational level in an effective manner. Methods: Three existing accounting methods (namely product related, process based, and monetary based) are connected within the hybrid approach. The potential to apply each method for an indirect activity is analyzed with regard to the system boundary requirements and availability of activity data and emission factors. The calculation procedures are introduced for selected activities. The advantages and limitations of the hybridization on organizational level are discussed. The developed approach is applied in a case study to the automotive supplier Brose Fahrzeugteile GmbH & Co.KG. Results and discussion: The framework for application of the hybrid approach including the required activity data and emission factors for every indirect activity and each accounting method is provided. The product-related and process-based methods are recommended as more robust; nevertheless, hybridization with the monetary-based method might be essential for compiling a comprehensive inventory by limited data availability. Such limitations as double counting, truncation error, and insufficient data resolution may influence the results and should be considered when applying the hybrid approach. The case study demonstrated that the proposed approach allowed establishing an inventory for all relevant indirect activities. However, due to missing emission factors, only the impact category climate change was calculated for all activities; acidification and water use were quantified for six activities. Conclusions: The introduced hybrid approach enables selecting the most suitable accounting method for the indirect activities depending on data availability. This promotes application of the organizational life cycle assessment in particular for small and medium enterprises and companies that do not have access to the commercial LCA datasets. Availability of the emission factors for all impact categories in public databases is essential to provide robust results using the hybrid approach

Data-driven exploration and continuum modeling of dislocation networks

The microstructural origin of strain hardening during plastic deformation in stage II deformation of face-centered cubic (fcc) metals can be attributed to the increase in dislocation density resulting in a formation of dislocation networks. Although this is a well known relation, the complexity of dislocation multiplication processes and details about the formation of dislocation networks have recently been revealed by discrete dislocation dynamics (DDD) simulations. It has been observed that dislocations, after being generated by multiplication mechanisms, show a limited expansion within their slip plane before they get trapped in the network by dislocation reactions. This mechanism involves multiple slip systems and results in a heterogeneous dislocation network, which is not reflected in most dislocation-based continuum models. We approach the continuum modeling of dislocation networks by using data science methods to provide a link between discrete dislocations and the continuum level. For this purpose, we identify relevant correlations that feed into a model for dislocation networks in a dislocation-based continuum theory of plasticity. As a key feature, the model combines the dislocation multiplication with the limitation of the travel distance of dislocations by formation of stable dislocation junctions. The effective mobility of the network is determined by a range of dislocation spacings which reproduces the scattering travel distances of generated dislocation as observed in DDD. The model is applied to a high-symmetry fcc loading case and compared to DDD simulations. The results show a physically meaningful microstructural evolution, where the generation of new dislocations by multiplication mechanisms is counteracted by a formation of a stable dislocation network. In conjunction with DDD, we observe a steady state interplay of the different mechanisms