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ENGINEERING (1240 journals)                  1 2 3 4 5 6 7 | Last

Showing 1 - 200 of 1205 Journals sorted alphabetically
3 Biotech     Open Access   (Followers: 8)
3D Research     Hybrid Journal   (Followers: 20)
AAPG Bulletin     Hybrid Journal   (Followers: 8)
AASRI Procedia     Open Access   (Followers: 14)
Abstract and Applied Analysis     Open Access   (Followers: 3)
Aceh International Journal of Science and Technology     Open Access   (Followers: 2)
ACS Nano     Full-text available via subscription   (Followers: 265)
Acta Geotechnica     Hybrid Journal   (Followers: 7)
Acta Metallurgica Sinica (English Letters)     Hybrid Journal   (Followers: 6)
Acta Polytechnica : Journal of Advanced Engineering     Open Access   (Followers: 3)
Acta Scientiarum. Technology     Open Access   (Followers: 3)
Acta Universitatis Cibiniensis. Technical Series     Open Access  
Active and Passive Electronic Components     Open Access   (Followers: 7)
Adaptive Behavior     Hybrid Journal   (Followers: 11)
Adıyaman Üniversitesi Mühendislik Bilimleri Dergisi     Open Access  
Adsorption     Hybrid Journal   (Followers: 4)
Advanced Engineering Forum     Full-text available via subscription   (Followers: 7)
Advanced Science     Open Access   (Followers: 5)
Advanced Science Focus     Free   (Followers: 5)
Advanced Science Letters     Full-text available via subscription   (Followers: 9)
Advanced Science, Engineering and Medicine     Partially Free   (Followers: 7)
Advanced Synthesis & Catalysis     Hybrid Journal   (Followers: 18)
Advances in Calculus of Variations     Hybrid Journal   (Followers: 2)
Advances in Catalysis     Full-text available via subscription   (Followers: 5)
Advances in Complex Systems     Hybrid Journal   (Followers: 6)
Advances in Engineering Software     Hybrid Journal   (Followers: 27)
Advances in Fuel Cells     Full-text available via subscription   (Followers: 15)
Advances in Fuzzy Systems     Open Access   (Followers: 5)
Advances in Geosciences (ADGEO)     Open Access   (Followers: 13)
Advances in Heat Transfer     Full-text available via subscription   (Followers: 21)
Advances in Human Factors/Ergonomics     Full-text available via subscription   (Followers: 23)
Advances in Magnetic and Optical Resonance     Full-text available via subscription   (Followers: 9)
Advances in Natural Sciences: Nanoscience and Nanotechnology     Open Access   (Followers: 29)
Advances in Operations Research     Open Access   (Followers: 12)
Advances in OptoElectronics     Open Access   (Followers: 5)
Advances in Physics Theories and Applications     Open Access   (Followers: 13)
Advances in Polymer Science     Hybrid Journal   (Followers: 43)
Advances in Porous Media     Full-text available via subscription   (Followers: 5)
Advances in Remote Sensing     Open Access   (Followers: 43)
Advances in Science and Research (ASR)     Open Access   (Followers: 4)
Aerobiologia     Hybrid Journal   (Followers: 2)
African Journal of Science, Technology, Innovation and Development     Hybrid Journal   (Followers: 6)
AIChE Journal     Hybrid Journal   (Followers: 35)
Ain Shams Engineering Journal     Open Access   (Followers: 5)
Akademik Platform Mühendislik ve Fen Bilimleri Dergisi     Open Access   (Followers: 1)
Alexandria Engineering Journal     Open Access   (Followers: 1)
AMB Express     Open Access   (Followers: 1)
American Journal of Applied Sciences     Open Access   (Followers: 26)
American Journal of Engineering and Applied Sciences     Open Access   (Followers: 10)
American Journal of Engineering Education     Open Access   (Followers: 9)
American Journal of Environmental Engineering     Open Access   (Followers: 16)
American Journal of Industrial and Business Management     Open Access   (Followers: 23)
Analele Universitatii Ovidius Constanta - Seria Chimie     Open Access  
Annals of Combinatorics     Hybrid Journal   (Followers: 3)
Annals of Pure and Applied Logic     Open Access   (Followers: 2)
Annals of Regional Science     Hybrid Journal   (Followers: 7)
Annals of Science     Hybrid Journal   (Followers: 7)
Antarctic Science     Hybrid Journal   (Followers: 1)
Applicable Algebra in Engineering, Communication and Computing     Hybrid Journal   (Followers: 2)
Applicable Analysis: An International Journal     Hybrid Journal   (Followers: 1)
Applied Catalysis A: General     Hybrid Journal   (Followers: 6)
Applied Catalysis B: Environmental     Hybrid Journal   (Followers: 18)
Applied Clay Science     Hybrid Journal   (Followers: 5)
Applied Computational Intelligence and Soft Computing     Open Access   (Followers: 11)
Applied Magnetic Resonance     Hybrid Journal   (Followers: 4)
Applied Nanoscience     Open Access   (Followers: 8)
Applied Network Science     Open Access   (Followers: 3)
Applied Numerical Mathematics     Hybrid Journal   (Followers: 5)
Applied Physics Research     Open Access   (Followers: 4)
Applied Sciences     Open Access   (Followers: 3)
Applied Spatial Analysis and Policy     Hybrid Journal   (Followers: 4)
Arabian Journal for Science and Engineering     Hybrid Journal   (Followers: 5)
Archives of Computational Methods in Engineering     Hybrid Journal   (Followers: 5)
Archives of Foundry Engineering     Open Access  
Archives of Thermodynamics     Open Access   (Followers: 8)
Arkiv för Matematik     Hybrid Journal   (Followers: 1)
ASEE Prism     Full-text available via subscription   (Followers: 3)
Asia-Pacific Journal of Science and Technology     Open Access  
Asian Engineering Review     Open Access  
Asian Journal of Applied Science and Engineering     Open Access   (Followers: 1)
Asian Journal of Applied Sciences     Open Access   (Followers: 2)
Asian Journal of Biotechnology     Open Access   (Followers: 8)
Asian Journal of Control     Hybrid Journal  
Asian Journal of Current Engineering & Maths     Open Access  
Asian Journal of Technology Innovation     Hybrid Journal   (Followers: 8)
Assembly Automation     Hybrid Journal   (Followers: 2)
at - Automatisierungstechnik     Hybrid Journal   (Followers: 1)
ATZagenda     Hybrid Journal  
ATZextra worldwide     Hybrid Journal  
Australasian Physical & Engineering Sciences in Medicine     Hybrid Journal   (Followers: 1)
Australian Journal of Multi-Disciplinary Engineering     Full-text available via subscription   (Followers: 2)
Autonomous Mental Development, IEEE Transactions on     Hybrid Journal   (Followers: 9)
Avances en Ciencias e Ingeniería     Open Access  
Balkan Region Conference on Engineering and Business Education     Open Access   (Followers: 1)
Bangladesh Journal of Scientific and Industrial Research     Open Access  
Basin Research     Hybrid Journal   (Followers: 5)
Batteries     Open Access   (Followers: 6)
Bautechnik     Hybrid Journal   (Followers: 1)
Bell Labs Technical Journal     Hybrid Journal   (Followers: 26)
Beni-Suef University Journal of Basic and Applied Sciences     Open Access   (Followers: 4)
BER : Manufacturing Survey : Full Survey     Full-text available via subscription   (Followers: 1)
BER : Motor Trade Survey     Full-text available via subscription  
BER : Retail Sector Survey     Full-text available via subscription   (Followers: 1)
BER : Retail Survey : Full Survey     Full-text available via subscription   (Followers: 1)
BER : Survey of Business Conditions in Manufacturing : An Executive Summary     Full-text available via subscription   (Followers: 2)
BER : Survey of Business Conditions in Retail : An Executive Summary     Full-text available via subscription   (Followers: 3)
Bhakti Persada : Jurnal Aplikasi IPTEKS     Open Access  
Bharatiya Vaigyanik evam Audyogik Anusandhan Patrika (BVAAP)     Open Access   (Followers: 1)
Biofuels Engineering     Open Access   (Followers: 1)
Biointerphases     Open Access   (Followers: 1)
Biomaterials Science     Full-text available via subscription   (Followers: 10)
Biomedical Engineering     Hybrid Journal   (Followers: 15)
Biomedical Engineering and Computational Biology     Open Access   (Followers: 13)
Biomedical Engineering Letters     Hybrid Journal   (Followers: 5)
Biomedical Engineering, IEEE Reviews in     Full-text available via subscription   (Followers: 19)
Biomedical Engineering, IEEE Transactions on     Hybrid Journal   (Followers: 35)
Biomedical Engineering: Applications, Basis and Communications     Hybrid Journal   (Followers: 5)
Biomedical Microdevices     Hybrid Journal   (Followers: 9)
Biomedical Science and Engineering     Open Access   (Followers: 4)
Biomedizinische Technik - Biomedical Engineering     Hybrid Journal  
Biomicrofluidics     Open Access   (Followers: 4)
BioNanoMaterials     Hybrid Journal   (Followers: 2)
Biotechnology Progress     Hybrid Journal   (Followers: 39)
Boletin Cientifico Tecnico INIMET     Open Access  
Botswana Journal of Technology     Full-text available via subscription   (Followers: 1)
Boundary Value Problems     Open Access   (Followers: 1)
Brazilian Journal of Science and Technology     Open Access   (Followers: 2)
Broadcasting, IEEE Transactions on     Hybrid Journal   (Followers: 10)
Bulletin of Canadian Petroleum Geology     Full-text available via subscription   (Followers: 13)
Bulletin of Engineering Geology and the Environment     Hybrid Journal   (Followers: 14)
Bulletin of the Crimean Astrophysical Observatory     Hybrid Journal  
Cahiers, Droit, Sciences et Technologies     Open Access  
Calphad     Hybrid Journal  
Canadian Geotechnical Journal     Hybrid Journal   (Followers: 31)
Canadian Journal of Remote Sensing     Full-text available via subscription   (Followers: 42)
Case Studies in Engineering Failure Analysis     Open Access   (Followers: 6)
Case Studies in Thermal Engineering     Open Access   (Followers: 5)
Catalysis Communications     Hybrid Journal   (Followers: 6)
Catalysis Letters     Hybrid Journal   (Followers: 2)
Catalysis Reviews: Science and Engineering     Hybrid Journal   (Followers: 7)
Catalysis Science and Technology     Free   (Followers: 8)
Catalysis Surveys from Asia     Hybrid Journal   (Followers: 3)
Catalysis Today     Hybrid Journal   (Followers: 7)
CEAS Space Journal     Hybrid Journal   (Followers: 2)
Cellular and Molecular Neurobiology     Hybrid Journal   (Followers: 3)
Central European Journal of Engineering     Hybrid Journal  
CFD Letters     Open Access   (Followers: 6)
Chaos : An Interdisciplinary Journal of Nonlinear Science     Hybrid Journal   (Followers: 2)
Chaos, Solitons & Fractals     Hybrid Journal   (Followers: 3)
Chinese Journal of Catalysis     Full-text available via subscription   (Followers: 2)
Chinese Journal of Engineering     Open Access   (Followers: 2)
Chinese Science Bulletin     Open Access   (Followers: 1)
Ciencia e Ingenieria Neogranadina     Open Access  
Ciencia en su PC     Open Access   (Followers: 1)
Ciencias Holguin     Open Access   (Followers: 2)
CienciaUAT     Open Access   (Followers: 1)
Cientifica     Open Access  
CIRP Annals - Manufacturing Technology     Full-text available via subscription   (Followers: 11)
CIRP Journal of Manufacturing Science and Technology     Full-text available via subscription   (Followers: 13)
City, Culture and Society     Hybrid Journal   (Followers: 20)
Clay Minerals     Full-text available via subscription   (Followers: 10)
Clean Air Journal     Full-text available via subscription   (Followers: 1)
Coal Science and Technology     Full-text available via subscription   (Followers: 3)
Coastal Engineering     Hybrid Journal   (Followers: 11)
Coastal Engineering Journal     Hybrid Journal   (Followers: 5)
Coatings     Open Access   (Followers: 4)
Cogent Engineering     Open Access   (Followers: 2)
Cognitive Computation     Hybrid Journal   (Followers: 4)
Color Research & Application     Hybrid Journal   (Followers: 2)
COMBINATORICA     Hybrid Journal  
Combustion Theory and Modelling     Hybrid Journal   (Followers: 14)
Combustion, Explosion, and Shock Waves     Hybrid Journal   (Followers: 13)
Communications Engineer     Hybrid Journal   (Followers: 1)
Communications in Numerical Methods in Engineering     Hybrid Journal   (Followers: 2)
Components, Packaging and Manufacturing Technology, IEEE Transactions on     Hybrid Journal   (Followers: 28)
Composite Interfaces     Hybrid Journal   (Followers: 7)
Composite Structures     Hybrid Journal   (Followers: 272)
Composites Part A : Applied Science and Manufacturing     Hybrid Journal   (Followers: 208)
Composites Part B : Engineering     Hybrid Journal   (Followers: 246)
Composites Science and Technology     Hybrid Journal   (Followers: 183)
Comptes Rendus Mécanique     Full-text available via subscription   (Followers: 2)
Computation     Open Access  
Computational Geosciences     Hybrid Journal   (Followers: 15)
Computational Optimization and Applications     Hybrid Journal   (Followers: 7)
Computational Science and Discovery     Full-text available via subscription   (Followers: 2)
Computer Applications in Engineering Education     Hybrid Journal   (Followers: 8)
Computer Science and Engineering     Open Access   (Followers: 19)
Computers & Geosciences     Hybrid Journal   (Followers: 30)
Computers & Mathematics with Applications     Full-text available via subscription   (Followers: 8)
Computers and Electronics in Agriculture     Hybrid Journal   (Followers: 5)
Computers and Geotechnics     Hybrid Journal   (Followers: 11)
Computing and Visualization in Science     Hybrid Journal   (Followers: 6)
Computing in Science & Engineering     Full-text available via subscription   (Followers: 33)
Conciencia Tecnologica     Open Access  
Concurrent Engineering     Hybrid Journal   (Followers: 3)
Continuum Mechanics and Thermodynamics     Hybrid Journal   (Followers: 8)
Control and Dynamic Systems     Full-text available via subscription   (Followers: 9)
Control Engineering Practice     Hybrid Journal   (Followers: 43)
Control Theory and Informatics     Open Access   (Followers: 8)
Corrosion Science     Hybrid Journal   (Followers: 25)

        1 2 3 4 5 6 7 | Last

  [SJR: 1.296]   [H-I: 38]   [0 followers]  Follow
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
   ISSN (Print) 1439-6912 - ISSN (Online) 0209-9683
   Published by Springer-Verlag Homepage  [2352 journals]
  • Asymptotic Metric Behavior of Random Cayley Graphs of Finite Abelian
    • Authors: Uri Shapira; Reut Zuck
      Abstract: Using methods of Marklof and Strömbergsson we establish several limit laws for metric parameters of random Cayley graphs of finite abelian groups with respect to a randomly chosen set of generators of a fixed size. Doing so we settle a conjecture of Amir and Gurel- Gurevich.
      PubDate: 2018-02-07
      DOI: 10.1007/s00493-017-3672-2
  • On the Size of K -Cross-Free Families
    • Authors: Andrey Kupavskii; János Pach; István Tomon
      Abstract: Two subsets A,B of an n-element ground set X are said to be crossing, if none of the four sets A∩B, A\B, B\A and X\(A∪B) are empty. It was conjectured by Karzanov and Lomonosov forty years ago that if a family F of subsets of X does not contain k pairwise crossing elements, then F =O(kn). For k=2 and 3, the conjecture is true, but for larger values of k the best known upper bound, due to Lomonosov, is F =O(knlogn). In this paper, we improve this bound for large n by showing that F =O k (nlog*n) holds, where log* denotes the iterated logarithm function.
      PubDate: 2018-02-07
      DOI: 10.1007/s00493-017-3792-8
  • Ramsey Graphs Induce Subgraphs of Many Different Sizes
    • Authors: Bhargav Narayanan; Julian Sahasrabudhe; István Tomon
      Abstract: A graph on n vertices is said to be C-Ramsey if every clique or independent set of the graph has size at most C logn. The only known constructions of Ramsey graphs are probabilistic in nature, and it is generally believed that such graphs possess many of the same properties as dense random graphs. Here, we demonstrate one such property: for any fixed C > 0, every C-Ramsey graph on n vertices induces subgraphs of at least n2-o(1) distinct sizes. This near-optimal result is closely related to two unresolved conjectures, the first due to Erdős and McKay and the second due to Erdős, Faudree and Sós, both from 1992.
      PubDate: 2018-02-07
      DOI: 10.1007/s00493-017-3755-0
  • Associahedra Via Spines
    • Authors: Carsten Lange; Vincent Pilaud
      Abstract: An associahedron is a polytope whose vertices correspond to triangulations of a convex polygon and whose edges correspond to flips between them. Using labeled polygons, C. Hohlweg and C. Lange constructed various realizations of the associahedron with relevant properties related to the symmetric group and the permutahedron. We introduce the spine of a triangulation as its dual tree together with a labeling and an orientation. This notion extends the classical understanding of the associahedron via binary trees, introduces a new perspective on C. Hohlweg and C. Lange’s construction closer to J.-L. Loday’s original approach, and sheds light upon the combinatorial and geometric properties of the resulting realizations of the associahedron. It also leads to noteworthy proofs which shorten and simplify previous approaches.
      PubDate: 2018-02-07
      DOI: 10.1007/s00493-015-3248-y
  • A Ramsey Statement for Infinite Groups
    • Authors: Péter Komjáth
      Abstract: If κ is a cardinal, n < ω, then there exists an Abelian group G such that if F : G→κ, then there exist distinct elements ai,α ∈ G (1≤i≤n, α<κ), and a color τ < κ such that if 1≤i0<⋯<i r ≤n, α1,...,α r <κ, then \(F\left( {{a_{{i_1},{\alpha _1}}} + \cdots + {a_{{i_r},{\alpha _r}}}} \right) = \tau \) .
      PubDate: 2018-02-03
      DOI: 10.1007/s00493-016-3706-1
  • Distance-Preserving Subgraphs of Johnson Graphs
    • Authors: Victor Chepoi
      Pages: 1039 - 1055
      Abstract: We give a characterization of distance-preserving subgraphs of Johnson graphs, i.e., of graphs which are isometrically embeddable into Johnson graphs (the Johnson graph J(m,∧) has the subsets of cardinality m of a set ∧ as the vertex-set and two such sets A,B are adjacent iff AΔB =2). Our characterization is similar to the characterization of D. Ž. Djoković [11] of distance-preserving subgraphs of hypercubes and provides an explicit description of the wallspace (split system) defining the embedding.
      PubDate: 2017-12-01
      DOI: 10.1007/s00493-016-3421-y
      Issue No: Vol. 37, No. 6 (2017)
  • Induced Subgraphs of Graphs with Large Chromatic Number. III. Long Holes
    • Authors: Maria Chudnovsky; Alex Scott; Paul Seymour
      Pages: 1057 - 1072
      Abstract: We prove a 1985 conjecture of Gyárfás that for all k, ℓ, every graph with sufficiently large chromatic number contains either a clique of cardinality more than k or an induced cycle of length more than ℓ.
      PubDate: 2017-12-01
      DOI: 10.1007/s00493-016-3467-x
      Issue No: Vol. 37, No. 6 (2017)
  • Integer 4-Flows and Cycle Covers
    • Authors: Genghua Fan
      Pages: 1097 - 1112
      Abstract: Let G be a bridgeless graph and denote by cc(G) the shortest length of a cycle cover of G. Let V2(G) be the set of vertices of degree 2 in G. It is known that if cc(G)≤1.4 E(G) for every bridgeless graph G with V2(G) ≤ \(\frac{1}{10}\) E(G) , then the Cycle Double Cover Conjecture is true. The best known result cc(G)≤ \(\frac{5}{3}\) E(G) (≈1.6667 E(G) ) was established over 30 years ago. Recently, it was proved that cc(G) ≤ \(\frac{44}{27}\) E(G) (≈ 1.6296 E(G) ) for loopless graphs with minimum degree at least 3. In this paper, we obtain results on integer 4-flows, which are used to find bounds for cc(G). We prove that if G has minimum degree at least 3 (loops being allowed), then cc(G)<1.6258 E(G) . As a corollary, adding loops to vertices of degree 2, we obtain that cc(G)<1.6466 E(G) for every bridgeless graph G with V2(G) ≤ \(\frac{1}{30}\) E(G) .
      PubDate: 2017-12-01
      DOI: 10.1007/s00493-016-3379-9
      Issue No: Vol. 37, No. 6 (2017)
  • On the Number of Edge-Disjoint Triangles in K 4 -Free Graphs
    • Authors: Ervin Győri; Balázs Keszegh
      Pages: 1113 - 1124
      Abstract: We prove the quarter of a century old conjecture that every K4-free graph with n vertices and [n2/4]+m edges contains m pairwise edge-disjoint triangles.
      PubDate: 2017-12-01
      DOI: 10.1007/s00493-016-3500-0
      Issue No: Vol. 37, No. 6 (2017)
  • Decomposing a Graph into Forests: The Nine Dragon Tree Conjecture is True
    • Authors: Hongbi Jiang; Daqing Yang
      Pages: 1125 - 1137
      Abstract: The fractional arboricity of a graph G, denoted by Γf (G), is defined as $${\Gamma _f}\left( G \right) = {\max _{H \subseteq G,v\left( H \right) > 1}}\frac{{e\left( H \right)}}{{v\left( H \right) - 1}}$$ . The celebrated Nash-Williams’ Theorem states that a graph G can be partitioned into at most k forests if and only if Γf (G)≤k. The Nine Dragon Tree (NDT) Conjecture [posed by Montassier, Ossona de Mendez, Raspaud, and Zhu, in “Decomposing a graph into forests”, J. Combin. Theory Ser. B 102 (2012) 38-52] asserts that if $${\Gamma _f}\left( G \right) \leqslant k + \frac{d}{{k + d + 1}}$$ , then G decomposes into k+1 forests with one having maximum degree at most d. In this paper, we prove the Nine Dragon Tree (NDT) Conjecture.
      PubDate: 2017-12-01
      DOI: 10.1007/s00493-016-3390-1
      Issue No: Vol. 37, No. 6 (2017)
  • On-Line Approach to Off-Line Coloring Problems on Graphs with Geometric
    • Authors: Tomasz Krawczyk; Bartosz Walczak
      Pages: 1139 - 1179
      Abstract: The main goal of this paper is to formalize and explore a connection between chromatic properties of graphs with geometric representations and competitive analysis of on-line algorithms, which became apparent after the recent construction of triangle-free geometric intersection graphs with arbitrarily large chromatic number due to Pawlik et al. We show that on-line graph coloring problems give rise to classes of game graphs with a natural geometric interpretation. We use this concept to estimate the chromatic number of graphs with geometric representations by finding, for appropriate simpler graphs, on-line coloring algorithms using few colors or proving that no such algorithms exist. We derive upper and lower bounds on the maximum chromatic number that rectangle overlap graphs, subtree overlap graphs, and interval filament graphs (all of which generalize interval overlap graphs) can have when their clique number is bounded. The bounds are absolute for interval filament graphs and asymptotic of the form (log logn)f(ω) for rectangle and subtree overlap graphs, where f(ω) is a polynomial function of the clique number and n is the number of vertices. In particular, we provide the first construction of geometric intersection graphs with bounded clique number and with chromatic number asymptotically greater than log logn. We also introduce a concept of K k -free colorings and show that for some geometric representations, K3-free chromatic number can be bounded in terms of clique number although the ordinary (K2-free) chromatic number cannot. Such a result for segment intersection graphs would imply a well-known conjecture that k-quasi-planar geometric graphs have linearly many edges.
      PubDate: 2017-12-01
      DOI: 10.1007/s00493-016-3414-x
      Issue No: Vol. 37, No. 6 (2017)
  • Proof of Schur’s Conjecture in ℝ D
    • Authors: Andrey B. Kupavskii; Alexandr Polyanskii
      Pages: 1181 - 1205
      Abstract: In this paper we prove Schur’s conjecture in ℝ d , which states that any diameter graph G in the Euclidean space ℝ d on n vertices may have at most n cliques of size d. We obtain an analogous statement for diameter graphs with unit edge length on a sphere S r d of radius \(r>1/\sqrt{2}\) . The proof rests on the following statement, conjectured by F. Morić and J. Pach: given two unit regular simplices Δ1, Δ2 on d vertices in ℝ d , either they share d-2 vertices, or there are vertices v1∈Δ1, v2∈Δ2 such that ‖v1-v2‖>1. The same holds for unit simplices on a d-dimensional sphere of radius greater than \(1/\sqrt{2}\) .
      PubDate: 2017-12-01
      DOI: 10.1007/s00493-016-3340-y
      Issue No: Vol. 37, No. 6 (2017)
  • Bipartite Kneser Graphs are Hamiltonian
    • Authors: Torsten Mütze; Pascal Su
      Pages: 1207 - 1219
      Abstract: For integers k ≥1 and n≥2k+1 the Kneser graph K(n;k) has as vertices all k-element subsets of [n]:={1;2;:::;n} and an edge between any two vertices (=sets) that are disjoint. The bipartite Kneser graph H(n,k) has as vertices all k-element and (n—k)-element subsets of [n] and an edge between any two vertices where one is a subset of the other. It has long been conjectured that all Kneser graphs and bipartite Kneser graphs except the Petersen graph K(5, 2) have a Hamilton cycle. The main contribution of this paper is proving this conjecture for bipartite Kneser graphs H(n,k). We also establish the existence of cycles that visit almost all vertices in Kneser graphs K(n,k) when n=2k+o(k), generalizing and improving upon previous results on this problem.
      PubDate: 2017-12-01
      DOI: 10.1007/s00493-016-3434-6
      Issue No: Vol. 37, No. 6 (2017)
  • The Number of Unit-Area Triangles in the Plane: Theme and Variation
    • Authors: Orit E. Raz; Micha Sharir
      Pages: 1221 - 1240
      Abstract: We show that the number of unit-area triangles determined by a set S of n points in the plane is O(n20/9), improving the earlier bound O(n9/4) of Apfelbaum and Sharir [2]. We also show, using a somewhat subtle construction, that if S consists of points on three lines, the number of unit-area triangles that S spans can be Ω(n2), for any triple of lines (it is always O(n2) in this case).
      PubDate: 2017-12-01
      DOI: 10.1007/s00493-016-3440-8
      Issue No: Vol. 37, No. 6 (2017)
  • Strong inapproximability results on balanced rainbow-colorable hypergraphs
    • Authors: Venkatesan Guruswami; Euiwoong Lee
      Abstract: Consider a K-uniform hypergraph H = (V, E). A coloring c: V → {1, 2, …, k} with k colors is rainbow if every hyperedge e contains at least one vertex from each color, and is called perfectly balanced when each color appears the same number of times. A simple polynomial-time algorithmnds a 2-coloring if H admits a perfectly balanced rainbow k-coloring. For a hypergraph that admits an almost balanced rainbow coloring, we prove that it is NP-hard to find an independent set of size ϵ, for any ϵ > 0. Consequently, we cannot weakly color (avoiding monochromatic hyperedges) it with O(1) colors. With k=2, it implies strong hardness for discrepancy minimization of systems of bounded set-size. One of our main technical tools is based on reverse hypercontractivity. Roughly, it says the noise operator increases q-norm of a function when q < 1, which is enough for some special cases of our results. To prove the full results, we generalize the reverse hypercontractivity to more general operators, which might be of independent interest. Together with the generalized reverse hypercontractivity and recent developments in inapproximability based on invariance principles for correlated spaces, we give a recipe for converting a promising test distribution and a suitable choice of an outer PCP to hardness of nding an independent set in the presence of highly-structured colorings. We use this recipe to prove additional results almost in a black-box manner, including: (1) the rst analytic proof of (K − 1 − ϵ)-hardness of K-Hypergraph Vertex Cover with more structure in completeness, and (2) hardness of (2Q+1)-SAT when the input clause is promised to have an assignment where every clause has at least Q true literals.
      PubDate: 2017-12-14
      DOI: 10.1007/s00493-016-3383-0
  • Extending factorizations of complete uniform hypergraphs
    • Authors: M. A. Bahmanian; Mike Newman
      Abstract: We consider when a given r-factorization of the complete uniform hypergraph on m vertices K m h can be extended to an s-factorization of K n h . The case of r = s = 1 was first posed by Cameron in terms of parallelisms, and solved by Häggkvist and Hellgren. We extend these results, which themselves can be seen as extensions of Baranyai's Theorem. For r=s, we show that the “obvious” necessary conditions, together with the condition that gcd(m,n,h)=gcd(n,h) are sufficient. In particular this gives necessary and sufficient conditions for the case where r=s and h is prime. For r<s we show that the obvious necessary conditions, augmented by gcd(m,n,h)=gcd(n,h), n≥2m, and \(1 \leqslant \frac{s}{r} \leqslant \frac{m}{k}\left[ {1 - \left( {\begin{array}{*{20}{c}} {m - k} \\ h \end{array}} \right)/\left( {\begin{array}{*{20}{c}} m \\ h \end{array}} \right)} \right]\) are sufficient, where k=gcd(m,n,h). We conclude with a discussion of further necessary conditions and some open problems.
      PubDate: 2017-12-09
      DOI: 10.1007/s00493-017-3396-3
  • Finding perfect matchings in bipartite hypergraphs
    • Authors: Chidambaram Annamalai
      Abstract: Haxell’s condition [14] is a natural hypergraph analog of Hall’s condition, which is a wellknown necessary and sufficient condition for a bipartite graph to admit a perfect matching. That is, when Haxell’s condition holds it forces the existence of a perfect matching in the bipartite hypergraph. Unlike in graphs, however, there is no known polynomial time algorithm to find the hypergraph perfect matching that is guaranteed to exist when Haxell’s condition is satisfied. We prove the existence of an efficient algorithm to find perfect matchings in bipartite hypergraphs whenever a stronger version of Haxell’s condition holds. Our algorithm can be seen as a generalization of the classical Hungarian algorithm for finding perfect matchings in bipartite graphs. The techniques we use to achieve this result could be of use more generally in other combinatorial problems on hypergraphs where disjointness structure is crucial, e.g., Set Packing.
      PubDate: 2017-12-09
      DOI: 10.1007/s00493-017-3567-2
  • Multiplicative bases and an Erdős problem
    • Authors: Péter Pál Pach; Csaba Sándor
      Abstract: In this paper we investigate how small the density of a multiplicative basis of order h can be in {1,2,...,n} and in ℤ+. Furthermore, a related problem of Erdős is also studied: How dense can a set of integers be, if none of them divides the product of h others'
      PubDate: 2017-12-09
      DOI: 10.1007/s00493-016-3588-2
  • On the linear span of lattice points in a parallelepiped
    • Authors: Marcel Celaya
      Abstract: Let Λ⊂R n be a lattice which contains the integer lattice Z n . We characterize the space of linear functions R n →R which vanish on the lattice points of Λ lying in the half-open unit cube [0, 1) n . We also find an explicit formula for the dimension of the linear span of Λ∩[0,1) n . The results in this paper generalize and are based on the Terminal Lemma of Reid, which is in turn based upon earlier work of Morrison and Stevens on the classification of four dimensional isolated Gorenstein terminal cyclic quotient singularities.
      PubDate: 2017-12-09
      DOI: 10.1007/s00493-017-3562-7
  • Black-box identity testing of depth-4 multilinear circuits
    • Authors: Shubhangi Saraf; Ilya Volkovich
      Abstract: We study the problem of identity testing for multilinear ΣΠΣΠ(k) circuits, i.e., multilinear depth-4 circuits with fan-in k at the top + gate. We give the first polynomial-time deterministic identity testing algorithm for such circuits when k=O(1). Our results also hold in the black-box setting. The running time of our algorithm is \({\left( {ns} \right)^{{\text{O}}\left( {{k^3}} \right)}}\) , where n is the number of variables, s is the size of the circuit and k is the fan-in of the top gate. The importance of this model arises from [11], where it was shown that derandomizing black-box polynomial identity testing for general depth-4 circuits implies a derandomization of polynomial identity testing (PIT) for general arithmetic circuits. Prior to our work, the best PIT algorithm for multilinear ΣΠΣΠ(k) circuits [31] ran in quasi-polynomial-time, with the running time being \({n^{{\rm O}\left( {{k^6}\log \left( k \right){{\log }^2}s} \right)}}\) . We obtain our results by showing a strong structural result for multilinear ΣΠΣΠ(k) circuits that compute the zero polynomial. We show that under some mild technical conditions, any gate of such a circuit must compute a sparse polynomial. We then show how to combine the structure theorem with a result by Klivans and Spielman [33], on the identity testing for sparse polynomials, to yield the full result.
      PubDate: 2017-12-09
      DOI: 10.1007/s00493-016-3460-4
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