Fast Parallel Reordering and Isomorphism Testing of k -Trees

In this paper two problems on the class of k -trees, a subclass of the class of chordal graphs, are considered: the fast reordering problem and the isomorphism problem. An O(log ² n) time parallel algorithm for the fast reordering problem is described that uses O(nk(n-k)/\kern -1ptlog n) processors on a CRCW PRAM proving membership in the class NC for fixed k . An O(nk(k+1)!) time sequential algorithm for the isomorphism problem is obtained representing an improvement over the O(n ² k(k+1)!) algorithm of Sekharan (the second author) [10]. A parallel version of this sequential algorithm is presented that runs in O(log ² n) time using O((nk((k+1)!+n-k))/log n) processors improving on a parallel algorithm of Sekharan for the isomorphism problem [10]. Both the sequential and parallel algorithms use a concept introduced in this paper called the kernel of a k -tree.     

Fast Parallel Reordering and Isomorphism Testing of k -Trees

Abstract. In this paper two problems on the class of k -trees, a subclass of the class of chordal graphs, are considered: the fast reordering problem and the isomorphism problem. An O(log ² n) time parallel algorithm for the fast reordering problem is described that uses O(nk(n-k)/\kern -1ptlog n) processors on a CRCW PRAM proving membership in the class NC for fixed k . An O(nk(k+1)!) time sequential algorithm for the isomorphism problem is obtained representing an improvement over the O(n ² k(k+1)!) algorithm of Sekharan (the second author) [10]. A parallel version of this sequential algorithm is presented that runs in O(log ² n) time using O((nk((k+1)!+n-k))/log n) processors improving on a parallel algorithm of Sekharan for the isomorphism problem [10]. Both the sequential and parallel algorithms use a concept introduced in this paper called the kernel of a k -tree.     

Multicast Routing with Delay and Delay Variation Constraints for Collaborative Applications on Overlay Networks

Computer supported collaborative applications on overlay networks are gaining popularity among users who are geographically dispersed. Examples of these kinds of applications include video-conferencing, distributed database replication, and online games. This type of application requires a multicasting subnetwork, using which messages should arrive at the destinations within a specified delay bound. These applications also require that destinations receive the message from the source at approximately the same time. The problem of finding a multicasting subnetwork with delay and delay-variation bound has been proved to be an NP complete problem in the literature and heuristics have been proposed for this problem. In this paper, we provide an efficient heuristic to obtain a multicast subnetwork on an overlay network, given a source and a set of destinations that is within a specified maximum delay and a specified maximum variation in the delays from a source to the destinations. The time-complexity of our algorithm is O(|E|+nk log(|E|/n)+m²k), where n and |E| are the number of nodes and edges in the network, respectively, k is the number of shortest paths determined, and m is the number of destinations. We have shown that our algorithm is significantly better in terms of time-complexity than existing algorithms for the same problem. Our extensive empirical studies indicate that our heuristic uses significantly less runtime in comparison with the best-known heuristics while achieving the tightest delay variation for a given end-to-end delay bound     

Enzyme-linked immunosorbent assay (ELISA) for the determination of the toxic glycoside cleistanthin B

Cleistanthus collinus is a highly toxic plant frequently implicated in suicidal and homicidal poisoning cases referred to our laboratory. An enzyme-linked immunosorbent assay (ELISA) is reported in this paper for the quantitation of the active principles of C. collinus. This method is highly reproducible and sensitive to detect as low as 2 ng/ml of cleistanthin B, a toxic constituent of C. collinus. The ELISA can be successfully applied for the specific identification of C. collinus poisoning in clinical and forensic toxicology.     

The Solid Particle Erosion Behavior of Carbon/Carbon and Carbon/Phenolic Composite Used in Re-entry Vehicles

Several engineering components made of carbon-based heat-resistant composites are subjected to severe erosive wear. In view of the above, the solid particle erosion behavior of two and four dimensionally reinforced carbon/carbon (C/C) composites as well as that of carbon/phenolic (C/P) composite has been characterized at the ambient temperature. The investigated C/C composites have been produced through a liquid-phase infiltration method followed by hot isostatic pressing, while the C/P composite prepegs have been cured inside an autoclave. The erosion rates of these composites have been determined for two different impact angles and two different impact velocities using silica sand with average particle diameter of 200 μm. The morphologies of as-received and eroded surfaces of test specimens have been examined with the help of scanning electron microscopy to understand the mechanism of material removal. The erosion response, erosion efficiency, and erosion micromechanisms of these composites have been studied in detail. While the erosion resistance of the C/P composite is found to be superior to that of the investigated C/C composites, the four dimensionally reinforced C/C composite have shown the highest erosion efficiency. All the composites have exhibited a semi-ductile erosion response. Their mechanical properties have little correlation with the erosion rates.     

Implementation of Distributed Floor Control Protocols on Overlay Networks

Collaborative multimedia applications (CMAs) on overlay networks are gaining popularity among users who are geographically dispersed. Examples of these kinds of applications include networked games and collaborative design and simulation. An important challenge in realizing CMAs is obtaining floor control, a problem in which the end-users compete among themselves to gain exclusive access to a shared resource. In this paper, we present deterministic and randomized distributed mechanisms for solving the floor control problem. In particular, we adapt the well-known MAC protocols viz. distributed queue dual bus (DQDB), ALOHA, and carrier sense multiple access (CSMA) as solutions for the floor control problem. Central to our adaptation is an algorithmic methodology that efficiently virtualizes the underlying network connecting the CMA participants so as to enhance the proposed solutions' performance. We present analytical and experimental studies on the performance of the proposed floor control protocols that bring out their essential characteristics.     

Protocol for Dynamic Ad-Hoc Networks Using Distributed Spanning Trees

A dynamic ad-hoc network consists of a collection of mobile hosts with frequently changing network topology. We propose a distributed algorithm that adapts to the topology by utilizing spanning trees in the regions where the topology is stable, and resorting to an intelligent flooding-like approach in highly dynamic regions of the network. Routing is performed using the spanning trees based a hold-and-forward or shuttling mechanisms. We introduce the notion of connectivity-through-time and the parameter holding-time as new fundamental concepts that can be used by ad-hoc routing algorithms. For various network connectivity scenarios we evaluate the impact of these concepts on the performance of ad-hoc routing algorithms. Using simulation, we study the throughput, reachability and message–reachability ratio of the proposed schemes under various connection/disconnection rates and holding times.