38249565
An extreme problem concerning k-arc-cyclic property for a class of tournaments
B. Alspach has proved that a regular tournament is arc-pancyclic. Zhu and Tian proved that if a tournament T = (V, A) with vertex set V, arc set A and order p satisfies that for any arc (vi, vj) of T, if d+(vj)+d-(vi)⩾p−2, then T is arc-pancyclic, where p⩾7. In this paper we study an extreme problem concerning the k-arc-cyclic property for a class of tournaments. 
 
We say that a tournament T=(V, A) satisfies the condition O(p, q) if d+(v)+d-(u)⩾p−q for any arc (u, v) of T, where q is a positive integer and |V|=p. Zhu, Tian, Chen and Zhang proved that if a tournament T satisfies the condition O(p, q) and p⩾3q+3, then T is arc-pancyclic. Let S(p, q) be the set{T=(V, A): T is a tournament with p vertices and T satisfies the condition O(p, q)}; let Ck(u, v) be the set {cycles of T with length k using the arc (u, v)}. The aim of this paper is that for a given integer q, we can find an integer m(q, k) such that if p⩾m(q, k), then for any T ϵ S(p, q), T is k-arc-cyclic; if p⩽m(q, k)−1, then there exists T ϵ S(p, q) such that T is not k-arc-cyclic. We have found that m(q, 4)=5q−7, and m(q, 5)=⌊p∗(q)⌋+1 or ⌈p∗(q)⌉+1, where p∗(q)=(1+312)q−(1+43·3 12).
4362564
More powerful closure operations on graphs
Abstract Bondy and Chvatal have observed the following result: G =( V , E ) is a simple graph of order n . If uv ∉ E and d ( u )+ d ( v )⩾ n , then G is Hamiltonian iff G + uv is Hamiltonian. Thus, we can obtain a graph C n ( G ), named the n -closure of G , from G by successively joining pairs of non-adjacent vertices whose degree sum is at least n . Therefore, G is Hamiltonian if C n ( G ) is Hamiltonian. Moreover, Bondy and Chvatal [2] generalized this idea to several properties on G . In the paper, we present some more powerful closure operations that extend the idea of Bondy and Chvatal.
3757616
Hamilton cycles in 1-tough triangle-free graphs
A graph G is called triangle-free if G has no induced K3 as a subgraph. We set σ3=min{∑i=13d(vi)|{v1,v2,v3} is an independent set of vertices in G}. In this paper, we show that if G is a 1-tough and triangle-free graph of order n with n⩽σ3, then G is hamiltonian.
20128924
Long path connectivity of regular graphs
Abstract Any pair of vertices in a 4-connected non-bipartite k -regular graph are joined by a Hamilton path or a path of length at least 3 k −6.
27692910
Dominating cycles in regular 3-connected graphs
Abstract Let G be a 3-connected, k -regular graph on at most 4 k vertices. We show that, for k ⩾63, every longest cycle of G is a dominating cycle. We conjecture that G is in fact hamiltonian.
1667264
Path extendability of claw-free graphs
Let G be a connected, locally connected, claw-free graph of order n and x,y be two vertices of G. In this paper, we prove that if for any 2-cut S of G, S@?{x,y}=@A, then each (x,y)-path of length less than n-1 in G is extendable, that is, for any path P joining x and y of length h(
5775560
Hierarchical Bloom filter arrays (HBA): a novel, scalable metadata management system for large cluster-based storage
An efficient and distributed scheme for file mapping or file lookup scheme is critical in decentralizing metadata management within a group of metadata servers. This work presents a technique called HBA (hierarchical Bloom filter arrays) to map file names to the servers holding their metadata. Two levels of probabilistic arrays, i.e., Bloom filter arrays, with different accuracies are used on each metadata server. One array, with lower accuracy and representing the distribution of the entire metadata, trades accuracy for significantly reduced memory overhead, while the other array, with higher accuracy, caches partial distribution information and exploits the temporal locality of file access patterns. Extensive trace-driven simulations have shown our HBA design to be highly effective and efficient in improving performance and scalability of file systems in clusters with 1,000 to 10,000 nodes (or superclusters).
20068677
A case study of parallel I/O for biological sequence search on Linux clusters
In this paper we analyze the I/O access patterns of a widely-used biological sequence search tool and implement two variations that employ parallel-I/O for data access based on PVFS (Parallel Virtual File System) and CEFT-PVFS (cost-effective fault-tolerant PVFS). Experiments show that the two variations outperform the original tool when equal or even fewer storage devices are used in the former. It is also found that although the performance of the two variations improves consistently when initially increasing the number of servers, this performance gain from parallel I/O becomes insignificant with further increase in server number. We examine the effectiveness of two read performance optimization techniques in CEFT-PVFS by using this tool as a benchmark. Performance results indicate: (1) doubling the degree of parallelism boosts the read performance to approach that of PVFS; and (2) skipping hot-spots can substantially improve the I/O performance when the load on data servers is highly imbalanced. The I/O resource contention due to the sharing of server nodes by multiple applications in a cluster has been shown to degrade the performance of the original tool and the variation based on PVFS by up to 10 and 21 folds, respectively; whereas, the variation based on CEFT-PVFS only suffered a two-fold performance degradation.
15780176
Understanding the design space of referencing in collaborative augmented reality environments
For collaborative environments to be successful, it is critical that participants have the ability to generate effective references. Given the heterogeneity of the objects and the myriad of possible scenarios for collaborative augmented reality environments, generating meaningful references within them can be difficult. Participants in co-located physical spaces benefit from non-verbal communication, such as eye gaze, pointing and body movement; however, when geographically separated, this form of communication must be synthesized using computer-mediated techniques. We have conducted an exploratory study using a collaborative building task of constructing both physical and virtual models to better understand inter-referential awareness -- or the ability for one participant to refer to a set of objects, and for that reference to be understood. Our contributions are not necessarily in presenting novel techniques, but in narrowing the design space for referencing in collaborative augmented reality. This study suggests collaborative reference preferences are heavily dependent on the context of the workspace.
536806
CEFT: A cost-effective, fault-tolerant parallel virtual file system
The vulnerability of computer nodes due to component failures is a critical issue for cluster-based file systems. This paper studies the development and deployment of mirroring in cluster-based parallel virtual file systems to provide fault tolerance and analyzes the tradeoffs between the performance and the reliability in the mirroring scheme. It presents the design and implementation of CEFT, a scalable RAID-10 style file system based on PVFS, and proposes four novel mirroring protocols depending on whether the mirroring operations are server-driven or client-driven, whether they are asynchronous or synchronous. The comparisons of their write performances, measured in a real cluster, and their reliability and availability, obtained through analytical modeling, show that these protocols strike different tradeoffs between the reliability and performance. Protocols with higher peak write performance are less reliable than those with lower peak write performance, and vice versa. A hybrid protocol is proposed to optimize this tradeoff.
35564489
Accelerated 2D Image Processing on GPUs
Graphics processing units (GPUs) in recent years have evolved to become powerful, programmable vector processing units. Furthermore, the maximum processing power of current generation GPUs is roughly four times that of current generation CPUs (central processing units), and that power is doubling approximately every nine months, about twice the rate of Moore's law. This research examines the GPU's advantage at performing convolutionbased image processing tasks compared to the CPU. Straight-forward 2D convolutions show up to a 130:1 speedup on the GPU over the CPU, with an average speedup in our tests of 59:1. Over convolutions performed with the highly optimized FFTW routines on the CPU, the GPU showed an average speedup of 18:1 for filter kernel sizes from 3x3 to 29x29.