2,045 research outputs found

    Resistance of a delta wing in a supersonic flow

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    The resistance of a delta wing at small angle of attack in supersonic conical flow with its leading edges within the Mach cone is calculated by a method that separates out the suction force

    DC Microgrid Modeling and Energy Storage Placement to Enhance System Stability

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    The work of this thesis represents a joint venture between the University of Wisconsin-Milwaukee and the University of Wisconsin-Madison. A DC microgrid is selected for the efficiency benefits, lack of reactive power in the system, and ease of connecting to an AC grid. The system modeling relies on physical parameters and industry standard methods for the estimation of loads and lines. An example model is created for the University of Wisconsin - Milwaukee\u27s Campus. Due to the high penetration of renewable energy sources in the example model, system stability is a concern. To help mitigate stability issues, analysis is performed to have the ideal placement of energy storage. The analysis relies heavily on the deep properties of the system such as Eigenvalues and system controllability. Energy storage placement is verified and evaluated with model simulations

    Full Scale Proton Beam Impact Testing of new CERN Collimators and Validation of a Numerical Approach for Future Operation

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    New collimators are being produced at CERN in the framework of a large particle accelerator upgrade project to protect beam lines against stray particles. Their movable jaws hold low density absorbers with tight geometric requirements, while being able to withstand direct proton beam impacts. Such events induce considerable thermo-mechanical loads, leading to complex structural responses, which make the numerical analysis challenging. Hence, an experiment has been developed to validate the jaw design under representative conditions and to acquire online results to enhance the numerical models. Two jaws have been impacted by high-intensity proton beams in a dedicated facility at CERN and have recreated the worst possible scenario in future operation. The analysis of online results coupled to post-irradiation examinations have demonstrated that the jaw response remains in the elastic domain. However, they have also highlighted how sensitive the jaw geometry is to its mounting support inside the collimator. Proton beam impacts, as well as handling activities, may alter the jaw flatness tolerance value by ±\pm 70 Ό{\mu}m, whereas the flatness tolerance requirement is 200 Ό{\mu}m. In spite of having validated the jaw design for this application, the study points out numerical limitations caused by the difficulties in describing complex geometries and boundary conditions with such unprecedented requirements.Comment: 22 pages, 17 figures, Prepared for submission to JINS

    Non locality, closing the detection loophole and communication complexity

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    It is shown that the detection loophole which arises when trying to rule out local realistic theories as alternatives for quantum mechanics can be closed if the detection efficiency η\eta is larger than η≄d1/22−0.0035d\eta \geq d^{1/2} 2^{-0.0035d} where dd is the dimension of the entangled system. Furthermore it is argued that this exponential decrease of the detector efficiency required to close the detection loophole is almost optimal. This argument is based on a close connection that exists between closing the detection loophole and the amount of classical communication required to simulate quantum correlation when the detectors are perfect.Comment: 4 pages Latex, minor typos correcte

    Partitioning Edge-Colored Hypergraphs into Few Monochromatic Tight Cycles

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    Confirming a conjecture of Gy®arf®as, we prove that, for all natural numbers k and r, the vertices of every r-edge-colored complete k-uniform hypergraph can be partitioned into a bounded number (independent of the size of the hypergraph) of monochromatic tight cycles. We further prove that, for all natural numbers p and r, the vertices of every r-edge-colored complete graph can be partitioned into a bounded number of pth powers of cycles, settling a problem of Elekes, Soukup, Soukup, and Szentmikl®ossy [Discrete Math., 340 (2017), pp. 2053–2069]. In fact we prove a common generalization of both theorems which further extends these results to all host hypergraphs of bounded independence number

    A Hilton-Milner theorem for vector spaces

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    We show for k = 2 that if q = 3 and n = 2k + 1, or q = 2 and n = 2k + 2, then any intersecting family F of k-subspaces of an n-dimensional vector space over GF(q) with nFÂżF F = 0 has size at most (formula). This bound is sharp as is shown by Hilton-Milner type families. As an application of this result, we determine the chromatic number of the corresponding q-Kneser graphs

    Chromatic number, clique subdivisions, and the conjectures of Haj\'os and Erd\H{o}s-Fajtlowicz

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    For a graph GG, let χ(G)\chi(G) denote its chromatic number and σ(G)\sigma(G) denote the order of the largest clique subdivision in GG. Let H(n) be the maximum of χ(G)/σ(G)\chi(G)/\sigma(G) over all nn-vertex graphs GG. A famous conjecture of Haj\'os from 1961 states that σ(G)≄χ(G)\sigma(G) \geq \chi(G) for every graph GG. That is, H(n)≀1H(n) \leq 1 for all positive integers nn. This conjecture was disproved by Catlin in 1979. Erd\H{o}s and Fajtlowicz further showed by considering a random graph that H(n)≄cn1/2/log⁥nH(n) \geq cn^{1/2}/\log n for some absolute constant c>0c>0. In 1981 they conjectured that this bound is tight up to a constant factor in that there is some absolute constant CC such that χ(G)/σ(G)≀Cn1/2/log⁥n\chi(G)/\sigma(G) \leq Cn^{1/2}/\log n for all nn-vertex graphs GG. In this paper we prove the Erd\H{o}s-Fajtlowicz conjecture. The main ingredient in our proof, which might be of independent interest, is an estimate on the order of the largest clique subdivision which one can find in every graph on nn vertices with independence number α\alpha.Comment: 14 page

    Access Structure Hiding Secret Sharing from Novel Set Systems and Vector Families

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    Secret sharing provides a means to distribute shares of a secret such that any authorized subset of shares, specified by an access structure, can be pooled together to recompute the secret. The standard secret sharing model requires public access structures, which violates privacy and facilitates the adversary by revealing high-value targets. In this paper, we address this shortcoming by introducing \emph{hidden access structures}, which remain secret until some authorized subset of parties collaborate. The central piece of this work is the construction of a set-system H\mathcal{H} with strictly greater than exp⁥(c1.5(log⁥h)2log⁥log⁥h)\exp\left(c \dfrac{1.5 (\log h)^2}{\log \log h}\right) subsets of a set of hh elements. Our set-system H\mathcal{H} is defined over Zm\mathbb{Z}_m, where mm is a non-prime-power, such that the size of each set in H\mathcal{H} is divisible by mm but the sizes of their pairwise intersections are not divisible by mm, unless one set is a subset of another. We derive a vector family V\mathcal{V} from H\mathcal{H} such that superset-subset relationships in H\mathcal{H} are represented by inner products in V\mathcal{V}. We use V\mathcal{V} to "encode" the access structures and thereby develop the first \emph{access structure hiding} secret sharing scheme. For a setting with ℓ\ell parties, our scheme supports 22ℓ/2−O(log⁡ℓ)+12^{2^{\ell/2 - O(\log \ell) + 1}} out of the 22ℓ−O(log⁡ℓ)2^{2^{\ell - O(\log \ell)}} total monotone access structures, and its maximum share size for any access structures is (1+o(1))2ℓ+1πℓ/2(1+ o(1)) \dfrac{2^{\ell+1}}{\sqrt{\pi \ell/2}}. The scheme assumes semi-honest polynomial-time parties, and its security relies on the Generalized Diffie-Hellman assumption.Comment: This is the full version of the paper that appears in D. Kim et al. (Eds.): COCOON 2020 (The 26th International Computing and Combinatorics Conference), LNCS 12273, pp. 246-261. This version contains tighter bounds on the maximum share size, and the total number of access structures supporte

    From Quantum Query Complexity to State Complexity

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    State complexity of quantum finite automata is one of the interesting topics in studying the power of quantum finite automata. It is therefore of importance to develop general methods how to show state succinctness results for quantum finite automata. One such method is presented and demonstrated in this paper. In particular, we show that state succinctness results can be derived out of query complexity results.Comment: Some typos in references were fixed. To appear in Gruska Festschrift (2014). Comments are welcome. arXiv admin note: substantial text overlap with arXiv:1402.7254, arXiv:1309.773
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