26819257
Enumeration of graph embeddings
Abstract For a finite connected simple graph G , let Γ be a group of graph automorphisms of G . Two 2-cell embeddings ι: G → S and j : G → S of a graph G into a closed surface S (orientable or nonorientable) are congruent with respect to Γ if there are a surface homeomorphism h : S → S and a graph automorphism γϵΓ such that h oι= j oγ. In this paper, we give an algebraic characterization of congruent 2-cell embeddings, from which we enumerate the congruence classes of 2-cell embeddings of a graph G into closed surfaces with respect to a group of automorphisms of G , not just the full automorphism group. Some applications to complete graphs are also discussed. As an orientable case, the oriented congruence of a graph G into orientable surfaces with respect to the full automorphism group of G was enumerated by Mull et al. (1988).
17462310
Bipartite covering graphs
Abstract In this paper we study when a bipartite graph is a covering of a non-bipartite graph. We give a characterization of all bipartite coverings in terms of factoring the covering map through the canonical double covering. We also consider regular bipartite coverings described in terms of voltage assignments. We give an algebraic characterization of such coverings involving the subgroup generated by voltages on closed walks of even length. This allows us to count the number of regular bipartite coverings for orders which are twice a prime.
26190362
Enumerating branched orientable surface coverings over a non-orientable surface
The isomorphism classes of several types of graph coverings of a graph have been enumerated by many authors [M. Hofmeister, Graph covering projections arising from finite vector space over finite fields, Discrete Math. 143 (1995) 87-97; S. Hong, J.H. Kwak, J.Lee, Regular graph coverings whose covering transformation groups have the isomorphism extention property, Discrete Math. 148 (1996) 85-105; J.H. Kwak, J.H. Chun, J. Lee, Enumeration of regular graph coverings having finite abelian covering transformation groups, SIAM J. Discrete Math. 11 (1998) 273-285; J.H. Kwak, J. Lee, Isomorphism classes of graph bundles, Canad. J. Math. XLII (1990) 747-761; J.H. Kwak, J. Lee, Enumeration of connected graph coverings, J. Graph Theory 23 (1996) 105-109]. Recently, Kwak et al [Balanced regular coverings of a signed graph and regular branched orientable surface coverings over a non-orientable surface, Discrete Math. 275 (2004) 177-193] enumerated the isomorphism classes of balanced regular coverings of a signed graph, as a continuation of an enumeration work done by Archdeacon et al [Bipartite covering graphs, Discrete Math. 214 (2000) 51-63] the isomorphism classes of branched orientable regular surface coverings of a non-orientable surface having a finite abelian covering transformation group. In this paper, we enumerate the isomorphism classes of connected balanced (regular or irregular) coverings of a signed graph and those of unbranched orientable coverings of a non-orientable surface, as an answer of the question raised by Liskovets [Reductive enumeration under mutually orthogonal group actions, Acta-Appl. Math. 52 (1998) 91-120]. As a consequence of these two results, we also enumerate the isomorphism classes of branched orientable surface coverings of a non-orientable surface. Acta-Appl. Math. 52 (1998) 91-120]. As a consequence of these two results, we also enumerate the isomorphism classes of branched orientable surface coverings of a non-orientable surface.
29011378
The achromatic number of the union of cycles
The achromatic number of a graph G is the largest number of colors which can be assigned to the vertices of G so that adjacent vertices get different colors and each pair of distinct colors appears on the ends of some edge. We show that the achromatic number of the disjoint union of k cycles of length l1, l2 ...., lk is equal to the achromatic number of the cycle of length p = Σi=1k li for any k ≤ √p/2, and that the achromatic number of the disjoint union of k triangles (resp. quadrangles) is equal to the achromatic number of the cycle of length 3k (resp. 4k) for any positive integer k.
47092701
Loop formulas for circumscription
Clark's completion is a simple nonmonotonic formalism and a special case of many nonmonotonic logics. Recently there has been work on extending completion with "loop formulas" so that general cases of nonmonotonic logics such as logic programs (under the answer set semantics) and McCain-Turner causal logic can be characterized by propositional logic in the form of "comple(ion + loop formulas". In this paper, we show that the idea is applicable to McCarthy's circumscription in the propositional case. We also show how to embed propositional circumscription in logic programs and in causal logic, inspired by the uniform characterization of "completion + loop formulas".
28720432
Image coding by fitting RBF-surfaces to subimages
In this paper, an image compression method based on a novel idea of surface fitting is proposed. An image is divided into sub-images using a quad tree according to the complexity of the image surface, which is a three-dimensional surface when the pixel values are considered as heights (z-values) defined on the x-y plane. Sub-image surfaces are approximated using a radial-basis function network (RBFN), and the parameters of the RBFN are stored as compressed image representation. This method has comparable performance and quality to the JPEG image compression technique.
393666
DAS: Intelligent Scheduling Systems for Shipbuilding
Daewoo Shipbuilding Company, one of the largest shipbuilders in the world, has experienced great deal of trouble with the planning and scheduling of its production process. To solve the problems, from 1991 to 1993, Korea Advanced Institute of Science and Technology (KAIST) and Daewoo jointly conducted the Daewoo Shipbuilding Scheduling (das) Project. To integrate the scheduling expert systems for shipbuilding, we used a hierarchical scheduling architecture. To automate the dynamic spatial layout of objects in various areas of the shipyard, we developed spatial scheduling expert systems. For reliable estimation of person-hour requirements, we implemented the neural network-based person-hour estimator. In addition, we developed the paneled-block assembly shop scheduler and the long-range production planner. For this large-scale project, we devised a phased development strategy consisting of three phases: (1) vision revelation, (2) data-dependent realization, and (3) prospective enhancement. The DAS systems were successfully launched in January 1994 and are actively being used as indispensable systems in the shipyard, resulting in significant improvement in productivity and visible and positive effects in many areas.
13494624
Security policies
A security policy is a high-level specification of the security properties that a given system should possess. It is a means for designers, domain experts and implementers to communicate with each other, and a blueprint that drives a project from design through implementation and validation. We offer a survey of the most significant security policy models in the literature, showing how “security” may mean very different things in different contexts, and we review some of the mechanisms typically used to implement a given security policy.
17895301
Optimal choice of data restructuring points
Maintaining access efficiency to a data base as updates and/or usage patterns change often requires restructuring the data base. While analytical methods are available for determining the optimal point to restructure, they assume the mean access cost is a smooth function of time or the number of accesses and can be measured exactly at any point in time. The access cost in practice often varies, at least in the short run, In a random manner. This implies a nonzero probability of deciding the optimal reorganization point has been reached when in fact it has not. Determination of the optimal reorganization point must take into account the random behavior of the access cost and the probability (and cost) of deciding too early or too late to perform the reorganization. A technique for choosing the optimal reorganization point subject to random variation in the access cost is developed and some examples are presented.