A mixed hypergraph consists of two families of edges: the C-edges and D-edges. In a coloring, every C-edge has at least two vertices of the same color, while every D-edge has at least two vertices colored differently....
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A mixed hypergraph consists of two families of edges: the C-edges and D-edges. In a coloring, every C-edge has at least two vertices of the same color, while every D-edge has at least two vertices colored differently. The largest and smallest possible numbers of colors in a coloring are termed the upper and lower chromatic number, (chi) over bar and chi, respectively. A mixed hypergraph is called uniquely colorable if it has precisely one coloring apart from the permutation of colors. We begin a systematic study of uniquely colorable mixed hypergraphs. In particular, we show that every colorable mixed hypergraph can be embedded into some uniquely colorable mixed hypergraph;we investigate the role of uniquely colorable subhypergraphs being separators, study recursive operations (orderings and subset contractions) and unique colorings, and prove that it is NP-hard to decide whether a mixed hypergraph is uniquely colorable. We also discuss the weaker property where the mixed hypergoraph has a unique coloring with (chi) over bar colors and a unique coloring with chi colors, where (chi) over bar > chi. The class of these "weakly uniquely colorable" mixed hypergraphs contains all uniquely colorable graphs in the usual sense. (C) 2002 Elsevier Science B.V. All rights reserved.
We present a new approach to the problem of matching 3-D curves. The approach has a low algorithmic complexity in the number of models, and can operate in the presence of noise and partial occlusions. Our method build...
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We present a new approach to the problem of matching 3-D curves. The approach has a low algorithmic complexity in the number of models, and can operate in the presence of noise and partial occlusions. Our method builds upon the seminal work of Kishon et al. (1990), where curves are first smoothed using B-splines, with matching based on hashing using curvature and torsion measures. However, we introduce two enhancements. We make use of nonuniform B-spline approximations, which permits us to better retain information at high curvature locations. The spline approximations are controlled (i.e., regularized) by making use of normal vectors to the surface in 3-D on which the curves lie, and by an explicit minimization of a bending energy. These measures allow a more accurate estimation of position, curvature, torsion, and Frenet frames along the curve. The computational complexity of the recognition process is relatively independent of the number of models and is considerably decreased with explicit use of the Frenet frame for hypotheses generation. As opposed to previous approaches, the method better copes with partial occlusion. Moreover, following a statistical study of the curvature and torsion covariances, we optimize the hash table discretization and discover improved invariants for recognition, different than the torsion measure. Finally, knowledge of invariant uncertainties is used to compute an optimal global transformation using an extended Kalman filter. We present experimental results using synthetic data and also using characteristic curves extracted from 3-D medical images. An earlier version of this article was presented at the 2nd European Conference on Computer Vision in Italy.
Information systems face many threats, such as covert channels, which declassify hidden information by, e.g., analyzing the program execution time. Such threats exist at various stages of the execution of instructions...
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Information systems face many threats, such as covert channels, which declassify hidden information by, e.g., analyzing the program execution time. Such threats exist at various stages of the execution of instructions. Even if software developers are able to neutralize these threats in source code, new attack vectors can arise in compiler-generated machine code from these representations. Existing approaches for preventing vulnerabilities have numerous restrictions related to both their functionality and the range of threats that can be found and removed. This study presents a technique for removing threats and generating safer code using dynamic compilation in an execution environment by combining information from program analysis of the malicious code and re-compiling such code to run securely. The proposed approach stores summary information in the form of rules that can be shared among analyses. The annotations enable us to conduct the analyses to mitigate threats. Developers can update the analyses and control the volume of resources that are allocated to perform these analyses by changing the precision. The authors' experiments show that the binary code created by applying the suggested method is of high quality.
The main problem in information storage has previously been how large amounts of data can be stored. However, the technological development over the years has been able to give rather satisfactory answers to this prob...
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The main problem in information storage has previously been how large amounts of data can be stored. However, the technological development over the years has been able to give rather satisfactory answers to this problem. Recently, the focus has shifted towards determining how stored information can be efficiently retrieved. This problem is addressed in an article by E. Yaakobi and J. Bruck (2012), where information retrieval in associative memories is studied. In this paper, we focus on the case where the retrieved information unit is unambiguous. In particular, we present characterizations and study various extremal properties of such associative memories. Moreover, the algorithmic complexity of certain naturally rising problems is considered. (C) 2015 Elsevier Inc. All rights reserved.
An inverse kinetic theory applying specifically to incompressible Newtonian fluids which permits us to avoid the N-2 algorithmic complexity of the Poisson equation for the fluid pressure is presented. The theory is ba...
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An inverse kinetic theory applying specifically to incompressible Newtonian fluids which permits us to avoid the N-2 algorithmic complexity of the Poisson equation for the fluid pressure is presented. The theory is based on the construction of a suitable kinetic equation in phase space, which permits us to determine exactly the fluid equations by means of the velocity moments of the kinetic distribution function. It is found that the fluid pressure can also be determined as a moment of the distribution function without solving the Poisson equation, as is usually required in direct solution methods for the incompressible fluid equations. Finally, the dynamical system, underlying the incompressible Navier-Stokes equations and advancing in time the fluid fields, has been also identified and proven to produce an unique set of fluid equations. (c) 2005 Elsevier B.V. All rights reserved.
The problem of iterative adjustments of the weights of a phased array with a look-direction constraint in the presence of jammers is presented. The technique described uses the adaptive conjugate method instead of the...
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The problem of iterative adjustments of the weights of a phased array with a look-direction constraint in the presence of jammers is presented. The technique described uses the adaptive conjugate method instead of the popularly used method of steepest descent to eliminate the jammer components, thus minimizing the error between the received signal and the actual one. This iterative method minimized the L/sub 2/ norm (the mean square error) and is guaranteed to converge in a finite number of steps which is not available for the present techniques utilized to solve this problem. Improvement in rate of convergence is thus achieved at the expense of algorithmic complexity.
We prove that the combinatorial optimization problem of determining the hull number of a partial cube is NP-complete. This makes partial cubes the minimal graph class for which NP-completeness of this problem is known...
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We prove that the combinatorial optimization problem of determining the hull number of a partial cube is NP-complete. This makes partial cubes the minimal graph class for which NP-completeness of this problem is known and improves earlier results in the literature. On the other hand we provide a polynomial-time algorithm to determine the hull number of planar partial cube quadrangulations. Instances of the hull number problem for partial cubes described include poset dimension and hitting sets for interiors of curves in the plane. To obtain the above results, we investigate convexity in partial cubes and obtain a new characterization of these graphs in terms of their lattice of convex subgraphs. This refines a theorem of Handa. Furthermore we provide a topological representation theorem for planar partial cubes, generalizing a result of Fukuda and Handa about tope graphs of rank 3 oriented matroids. (C) 2015 Elsevier B.V. All rights reserved.
Various efforts to integrate biological knowledge into networks of interactions have produced a lively microbial systems biology. Putting molecular biology and computer sciences in perspective, we review another trend...
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Various efforts to integrate biological knowledge into networks of interactions have produced a lively microbial systems biology. Putting molecular biology and computer sciences in perspective, we review another trend in systems biology, in which recursivity and information replace the usual concepts of differential equations, feedback and feedforward loops and the like. Noting that the processes of gene expression separate the genome from the cell machinery, we analyse the role of the separation between machine and program in computers. However, computers do not make computers. For cells to make cells requires a specific organization of the genetic program, which we investigate using available knowledge. Microbial genomes are organized into a paleome (the name emphasizes the role of the corresponding functions from the time of the origin of life), comprising a constructor and a replicator, and a cenome (emphasizing community-relevant genes), made up of genes that permit life in a particular context. The cell duplication process supposes rejuvenation of the machine and replication of the program. The paleome also possesses genes that enable information to accumulate in a ratchet-like process down the generations. The systems biology must include the dynamics of information creation in its future developments.
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