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As the automotive industry shifts toward hybrid and alternative drive concepts like electromobility, it remains vital to continuously improve internal combustion technology. Internal combustion applications represent the largest portion of transportation technologies. Continuous development and improvement of passenger car engines focus on reducing emission by weight reduction and enhanced efficiency. To gain a competitive advantage in present and future engines, Mercedes-Benz AG developed the innovative NANOSLIDE® technology that uses thermal spray technology, i.e., twin wire arc spray, to coat the internal diameter of cylinder bores. Computational fluid dynamics (CFD) simulation is utilized to investigate the complex gas flow in the cylinder bore of the crankcase during the coating process. Extensively experiments are performed and analyzed to compare the results with the quantitative analysis in order to enhance the properties of the cylinder coating. The combination of simulation and coating experiments led to the development of uniform distributed layer adhesion strength throughout the length of the cylinder bore. [ABSTRACT FROM AUTHOR]

We obtain an effective enumeration of the family of finitely generated groups admitting a faithful, properly discontinuous action on some 2-manifold contained in the sphere. This is achieved by introducing a type of group presentation capturing exactly these groups. Extending this in a companion paper, we find group presentations capturing the planar finitely generated Cayley graphs. Thus we obtain an effective enumeration of these Cayley graphs, yielding in particular an affirmative answer to a question of Droms et al. [ABSTRACT FROM AUTHOR]

Most stream ciphers are vulnerable against generic time-memory-data tradeoff (TMD-TO) attacks, which reduce their effective key length to the birthday bound n/2, where n denotes the inner state length of the underlying keystream generator. This implies the necessity of a comparatively large inner state length for practical stream ciphers (e.g., n=288 and n=160 for the eSTREAM portfolio members Trivium and Grain v1, respectively). In this paper, we propose and analyze the LIZARD-construction, a new way to build stream ciphers. We prove a tight 2n/3 bound on its security against TMD-TO key recovery attacks, where the security lower bound refers to chosen-IV attacks. The security against TMD-TO distinguishing attacks remains at the birthday-bound level n/2. The lower bound refers to a random oracle model which allows to derive formal security results w.r.t. generic TMD-TO attacks. While similar frameworks have already been widely used for analyzing the security of block cipher, MAC, and hash function constructions, to the best of our knowledge this is the first time that such a model is considered in the context of stream ciphers. The security analysis presented in this paper is also of immediate practical relevance as, with the stream cipher LIZARD, a first instantiation of our new design principle (which we hence named LIZARD-construction) was introduced at FSE 2017. LIZARD has an inner state length of only 121 bits and surpasses Grain v1, the most hardware efficient member of the eSTREAM portfolio, in important metrics for lightweight ciphers such as chip area and power consumption. [ABSTRACT FROM AUTHOR]

Time-memory-data (TMD) tradeoff attacks limit the security level of many classical stream ciphers to the birthday bound. Very recently, a new field of research has emerged, which searches for so-called small-state stream ciphers that try to overcome this limitation. In this paper, existing designs and known analysis of small-state stream ciphers are revisited and new insights on distinguishers and key recovery are derived based on TMD tradeoff attacks. A particular result is the transfer of a generic distinguishing attack suggested in 2007 by Englund et al. to this new class of lightweight ciphers. Our analysis shows that the initial hope of achieving full security against TMD tradeoff attacks by continuously using the secret key has failed. In particular, we provide generic distinguishers for Plantlet and Fruit with complexity significantly smaller than that of exhaustive key search. However, by studying the assumptions underlying the applicability of these attacks, we are able to come up with a new design idea for small-state stream ciphers, which might allow to finally achieve full security against TMD tradeoff attacks. Another contribution of this paper is the first key recovery attack against the most recent version of Fruit. We show that there are at least 264 weak keys, each of which does not provide 80-bit security as promised by designers. [ABSTRACT FROM AUTHOR]

We prove that the cut space of any transitive graph G is a finitely generated Aut(G)-module if the same is true for its cycle space. This confirms a conjecture of Diestel which says that every locally finite transitive graph whose cycle space is generated by cycles of bounded length is accessible. In addition, it implies Dunwoody’s conjecture that locally finite hyperbolic transitive graphs are accessible. As a further application, we obtain a combinatorial proof of Dunwoody’s accessibility theorem of finitely presented groups. [ABSTRACT FROM AUTHOR]

Inside any proper hyperbolic geodesic space X we construct a rooted topological R-tree T that reflects the geometry of X in the following sense. All rays in T are quasi-geodesic in X. Every geodesic ray in X lies eventually close to a ray of T . The embedding of T in X extends continuously to their boundaries in a finite-to-one way, the number of boundary points of T mapping to a given boundary point of X being bounded if the (Assouad) dimension of the boundary of X is finite. [ABSTRACT FROM AUTHOR]

We look at group actions on graphs and other metric spaces, e. g., at group actions on geodesic hyperbolic spaces. We classify the types of automorphisms on these spaces and prove several results about the density of the hyperbolic limit set of the group in the whole limit set of the group. [ABSTRACT FROM AUTHOR]

We classify the finite connected-homogeneous digraphs, as well as the infinite locally finite such digraphs with precisely one end. This completes the classification of all the locally finite connected-homogeneous digraphs. [ABSTRACT FROM AUTHOR]

Diestel and Müller showed that the connected tree-width of a graph G, i.e., the minimum width of any tree-decomposition with connected parts, can be bounded in terms of the tree-width of G and the largest length of a geodesic cycle in G. We improve their bound to one that is of the correct order of magnitude. Finally, we construct a graph whose connected tree-width exceeds the connected order of any of its brambles. This disproves a conjecture by Diestel and Müuller asserting an analogue of tree-width duality. [ABSTRACT FROM AUTHOR]

We construct spanning trees in locally finite hyperbolic graphs that represent their hyperbolic compactification in a good way: so that the tree has at least one but at most a bounded number of disjoint rays to each boundary point. As a corollary we extend a result of Gromov which says that from every hyperbolic graph with bounded degrees one can construct a tree (disjoint from the graph) with a continuous surjection from the ends of the tree onto the hyperbolic boundary such that the surjection is finite-to-one. We shall construct a tree with these properties as a subgraph of the hyperbolic graph, which in addition is also a spanning tree of that graph. [ABSTRACT FROM AUTHOR]

We classify the connected-homogeneous digraphs with more than one end. We further show that if their underlying undirected graph is not connected-homogeneous, they are highly-arc-transitive. [ABSTRACT FROM AUTHOR]

We study transitivity properties of graphs with more than one end. We completely classify the distance-transitive such graphs and, for all k≥3, the k-CS-transitive such graphs. [ABSTRACT FROM AUTHOR]

We show that there is no one-ended, locally finite, planar, hyperbolic graph such that the stabilizer of one of its hyperbolic boundary points acts transitively on the vertices of the graph. This gives a partial answer to a question by Kaimanovich and Woess. [ABSTRACT FROM AUTHOR]

We investigate the structure of connected graphs, not necessarily locally finite, with infinitely many ends. We study end-transitive such graphs and such graphs with the property that the stabilizer of some end acts transitively on the vertices of the graph. In both cases we show that the graphs have a tree-like structure. [ABSTRACT FROM AUTHOR]