44940446
Weak bipolarizable graphs
We characterize a new class of perfectly orderable graphs and give a polynomial-time recognition algorithm, together with linear-time optimization algorithms for this class of graphs.
37426117
On the Closure of Triangle-Free Graphs Under Substitution
On dit qu'un graphe G se construit a partir de deux graphes G 1 et G 2 par substitution,si,pour un sommet donne w de G 1 ,G apparait en supprimant w et en rendant,par la suite,les sommets de G 2 adjacents a tous les voisins de w dans G 1 .On presente ici une caracterisation par configurations interdites de la fermeture de graphes sans triangles sous substitution.
39112817
Asteroidal Triple-Free Graphs
An independent set of three vertices such that each pair is joined by a path that avoids the neighborhood of the third is called an asteroidal triple. A graph is asteroidal triple-free (AT-free) if it contains no asteroidal triples. The motivation for this investigation was provided, in part, by the fact that the AT-free graphs provide a common generalization of interval, permutation, trapezoid, and cocomparability graphs. The main contribution of this work is to investigate and reveal fundamental structural properties of AT-free graphs. Specifically, we show that every connected AT-free graph contains a dominating pair, that is, a pair of vertices such that every path joining them is a dominating set in the graph. We then provide characterizations of AT-free graphs in terms of dominating pairs and minimal triangulations. Subsequently, we state and prove a decomposition theorem for AT-free graphs. An assortment of other properties of AT-free graphs is also provided. These properties generalize known structural properties of interval, permutation, trapezoid, and cocomparability graphs.
205001978
A Linear Time Algorithm to Compute a Dominating Path in an AT-Free Graph
Abstract An independent set { x , y , z } is called an asteroidal triple if between any pair in the triple there exists a path that avoids the neighborhood of the third. A graph is referred to as AT-free if it does not contain an asteroidal triple. We present a simple linear-time algorithm to compute a dominating path in a connected AT-free graph.
9433006
No antitwins in minimal imperfect graphs
Abstract It is customary to call vertices x and y twins if every vertex distinct from x and y is adjacent either to both of them or to neither of them. By analogy, we shall call vertices x and y antitwins if every vertex distinct from x and y is adjacent to precisely one of them. Lovasz proved that no minimal imperfect graph has twins. The purpose of this note is to prove the analogous statement for antitwins.
5840834
Asteroidal Triple-Free Graphs
Many families of perfect graphs such as interval graphs, permutation graphs, trapezoid graphs and cocomparability graphs demonstrate a type of linear ordering of their vertex sets. These graphs are all subfamilies of a class of graphs called the asteroidal triple-free graphs. (An independent triple {x, y, z} is called an asteroidal triple (AT, for short) if between any pair in the triple there exists a path that avoids the neighbourhood of the third vertex.) In this paper we argue that the property of being AT-free is what is enforcing the linear ordering of the vertex sets. To justify this claim, we present various structural properties and characterizations of AT-free graphs.
6823924
Some observations on using meta-heuristics for efficient location management in mobile computing networks
With the increase in global wireless communication, there is a need for efficient network management strategies. Location management in a mobile network involves keeping track of mobile host (MH) cell locations. MHs perform location updates to inform the network of their location. When a call arrives for an MH, the network uses its last known cell location and a paging strategy to find that host. Current location management techniques do not consider host-mobility patterns or call arrival rates. This paper describes a selective update strategy that is modeled on the characteristics of a network, such as, topology, host mobility patterns and connection request rates. Then, a genetic algorithm is used to solve the location management problem that involves the search of a large solution space. The aim of the work is to determine whether genetic algorithms can be applied successfully to solve this problem, and to evaluate their efficiency in solving this class of optimization problems. Results from the selective update strategy show improvements over alternative algorithms. The location management optimization problem is shown to be well adapted to the workings of the genetic algorithm. The proposed solution also saves power, processing time, and network bandwidth.
5533650
The hierarchical cliques interconnection network
The fully connected network possesses extremely good topological, fault-tolerant, and embedding properties. However, due to its high degree, the fully connected network has not been an attractive candidate for building parallel computers. On the other hand, tree-based networks are popular as parallel computer networks, even though they suffer from poor fault-tolerance and embedding properties. The hierarchical cliques interconnection network described in this paper incorporates positive features of the fully connected network and the tree network. In other words, the hierarchical cliques possess such desirable properties as low diameter, low degree, self routing, versatile embedding, good fault-tolerance and strong resilience. Hierarchical cliques can efficiently embed most important networks and possess a scalable, modular structure. Further, by combining hierarchical cliques with fat trees congestion in the upper levels can be alleviated.
44759030
Media access using dynamic bandwidth system to improve satellite network uplink performance
The paper describes a media access system for satellite network uplinks. The media access protocol is designed to support a range of low-level protocols using a dual-framing system, that is, there is a synchronous traffic subframe in which registered station requests are assigned fixed blocks or slots and an asynchronous traffic subframe for unregistered station random access on a contention basis. Slots for the registered stations are assigned through request to the satellite; the remaining frame time is assigned to unregistered stations. Capacity waste through contention resulting in collisions is minimized. The system uses dynamic bandwidth (bit rate) allocation for each channel, that is, the base frequency and bandwidth are changed for each channel at frame boundaries. The total bandwidth for the sum of all uplink channels is fixed. Channels that have low load based upon their request in a prior uplink frame are assigned lower bandwidth, while those with higher loading are provided larger bandwidth. By sharing bandwidth over channels at frame boundaries, overall network efficiency and fairness are significantly enhanced. Bandwidth allocation is decided in the satellite. It allocates sufficient bandwidth for all synchronous traffic and then commits the remaining bandwidth to asynchronous traffic. Here, the allocation for asynchronous traffic provides each channel with sufficient slots so that equal probability of success for stations sharing the channel can be expected. The combination of traffic assignment and bandwidth allocation provides significant improvement in overall network efficiency and fairness for all traffic types. The hardware implementation of media access for variable bandwidth sharing between channels use the concepts of Digital Software Radio. Copyright © 2003 John Wiley & Sons, Ltd.
31459718
Sequential and Parallel Meta-Heuristics for Solving the Single Row Routing Problem
The design of multi-layer printed circuit boards is vital in the construction of complex electronic systems. Wire routing is a crucial step in the overall design process, which can be decomposed into a number of single row routing (SRR) problems. This paper proposes an approach to solve the SRR problem based on parallel meta-heuristics. The development of this technique involves the design of an encoding strategy that allows all possible routings to be uniquely represented and the derivation of cost functions that maximizes the quality of the developed solutions. Further, parallelization of the proposed approach is attempted to improve the computational efficiency. The different stages of the development are backed by experiments to show the pros and cons of the sequential and parallel implementations.
45508612
A unifying look at clustering in mobile ad hoc networks
In recent years, a significant number of clustering schemes have been proposed in the literature. Most of them treat cluster initialization and cluster maintenance differently as if they were two entirely different undertakings. The main contribution of this work is a unifying way of looking at clustering in MANET. We make an important point: there is no difference between cluster initialization and cluster maintenance, and one algorithm should gracefully blend into the other. To illustrate the feasibility of this concept, we propose a novel tree-based clustering algorithm for MANET based on a number of properties of diameter-2 graphs. The algorithm is cluster-centric and, unlike the vast majority of algorithms in the literature, works in the presence of node mobility. Extensive simulation results show the effectiveness of our algorithm when compared to other clustering schemes proposed in the recent literature. Copyright © 2004 John Wiley & Sons, Ltd.