Leaps: an approach to the block structure of a graph

To study the block structure of a connected graph G=(V,E), we introduce two algebraic approaches that reflect this structure: a binary operation + called a leap operation and a ternary relation L called a leap system, both on a finite, nonempty set V. These algebraic structures are easily studied by considering their underlying graphs, which turn out to be block graphs. Conversely, we define the operation +G as well as the set of leaps LG of the connected graph G. The underlying graph of +G , as well as that of LG , turns out to be just the block closure of G (i.e. the graph obtained by making each block of G into a complete subgraph).

Guides and Shortcuts in Graphs

The geodesic structure of a graphs appears to be a very rich structure. There are many ways to describe this structure, each of which captures only some aspects. Ternary algebras are for this purpose very useful and have a long tradition. We study two instances: signpost systems, and a special case of which, step systems. Signpost systems were already used to characterize graph classes. Here we use these for the study of the geodesic structure of a spanning subgraph F with respect to its host graph G. Such a signpost system is called a guide to (F,G). Our main results are: the characterization of the step system of a cycle, the characterization of guides for spanning trees and hamiltonian cycles

Axiomatic characterization of the interval function of a graph

A fundamental notion in metric graph theory is that of the interval function I : V × V → 2V – {∅} of a (finite) connected graph G = (V,E), where I(u,v) = { w | d(u,w) + d(w,v) = d(u,v) } is the interval between u and v. An obvious question is whether I can be characterized in a nice way amongst all functions F : V × V -> 2V – {∅}. This was done in [13, 14, 16] by axioms in terms of properties of the functions F. The authors of the present paper, in the conviction that characterizing the interval function belongs to the central questions of metric graph theory, return here to this result again. In this characterization the set of axioms consists of five simple, and obviously necessary, axioms, already presented in [9], plus two more complicated axioms. The question arises whether the last two axioms are really necessary in the form given or whether simpler axioms would do the trick. This question turns out to be non-trivial. The aim of this paper is to show that these two supplementary axioms are optimal in the following sense. The functions satisfying only the five simple axioms are studied extensively. Then the obstructions are pinpointed why such functions may not be the interval function of some connected graph. It turns out that these obstructions occur precisely when either one of the supplementary axioms is not satisfied. It is also shown that each of these supplementary axioms is independent of the other six axioms. The presented way of proving the characterizing theorem (Theorem 3 here) allows us to find two new separate ``intermediate'' results (Theorems 1 and 2). In addition some new characterizations of modular and median graphs are presented. As shown in the last section the results of this paper could provide a new perspective on finite connected graphs

Leaps: an approach to the block structure of a graph

To study the block structure of a connected graph G=(V,E), we introduce two algebraic approaches that reflect this structure: a binary operation + called a leap operation and a ternary relation L called a leap system, both on a finite, nonempty set V. These algebraic structures are easily studied by considering their underlying graphs, which turn out to be block graphs. Conversely, we define the operation +G as well as the set of leaps LG of the connected graph G. The underlying graph of +G , as well as that of LG , turns out to be just the block closure of G (i.e. the graph obtained by making each block of G into a complete subgraph)

Bristol Bay Cooperative Management Plan Impact Assessment

U.S. Fish and Wildlife Servic

Western Gulf of Alaska Petroleum Development Scenarios: Economic and Demographic Impacts

The State of Alask

The Growth of the Alaskan Economy: Future Conditions Without the Proposal

The State of Alask

Economic and Demographic Systems Analysis, North Slope Borough

This report describes current and projected economic conditions in the North Slope Borough and discusses possible impacts of OCS development upon the Borough's revenues and expenditures as well as on Inupiat employment. We use a simulation model of the North Slope Borough's economy to examine these impacts. The North Slope Borough receives substantial revenues from its taxes on oil and gas property. Following our examination of the factors affecting borough revenues, we conclude that OCS development will not substantially increase borough revenues due to state-imposed property tax revenue limits. Other factors, however, can be expected to cause the borough to begin to curtail its construction program and, thereby, reduce local employment opportunities. Our review of Inupiat employment patterns and projected borough employment opportunities suggests that reduced Inupiat employment, rather than increased Inupiat involvement in petroleum activities, may best characterize the coming decade unless there are spec if i c efforts to reduce constraints to Inupiat employment associated with petroleum development. These constraints include job rotation schedules, work crew composition, hiring location, and training opportunities.Department of the Interior, Minerals Management Service, Alaska Outer Continental Shelf Region in the interest of informational exchange. Contract number 29058Ye

Alaska OCS Socioeconomic Studies Program

The State of Alask