1,721,296 research outputs found
ECEM: an event correlation based event manager for an I/O-intensive application
No full textIn Internet servers that run on general purpose operating systems, network subsystems and disk subsystems cooperate with each other for user requests. Many studies have focused on optimizing the data movement across the subsystems to reduce data copying overhead among kernel buffers, a network send buffer and a disk buffer. When data are moved across the subsystems, events such as read requests and write requests for data movement are also delivered across the subsystems by the servers and the operating system. However. there have been fewer Studies on the optimization of event delivery across the subsystems. In conventional operating systems, an event from a disk subsystem is delivered to a network subsystem regardless of the status of the network subsystem. If the network Subsystem is not ready for data sending, the execution of the server will be blocked, which causes scheduling and context switching overheads. This non-contiguous execution will incur deficiencies such as avoidable process blocking, context switching, cache pollution and long response time. To alleviate the deficiencies, we have developed inter-subsystem event delivery mechanisms that define event dependencies among the subsystems involved. We define an event correlation based on the happened-before relation. We propose deferred event delivery (DED) and disk-to-network splicing (DNS) to suppress scheduling and context switching during I/O request processing. We performed experiments on Linux 2.4 and the experimental results show that the number of context switching is reduced by up to 20% and server data transmit rate is improved by 4.0-8.1%. (C) 2003 Elsevier Inc. All rights reserved
A fast path planning by path graph optimization
No full textIn this paper, a fast path planning method by optimization of a path graph for both efficiency and accuracy is proposed. A conventional quadtree-based path planning approach is simple, robust, and efficient. However, it has two limitations. The first limitation is that many small cells are required to represent obstacles because the positions and shapes of the cells are not object-dependent and searching the shortest path in the path graph is slow. The second limitation is generation of nonoptimal paths due to large cells in a free space. The cost of traversing a cell is the same whether a path just clips a corner of the cell or actually passes through the entire width of the cell. The quadtree is very sensitive to obstacle placement and the error factor is proportional to the size of the cell. We propose a path graph optimization technique employing a compact mesh representation. A world space is triangulated into a base mesh and the base mesh is simplified to a compact mesh. The compact mesh representation is object-dependent; the positions of vertexes of the mesh are optimized according to the curvatures of the obstacles. The compact mesh represents the obstacles as accurately as the quadtree even though using much fewer vertexes than the quadtree. The compact mesh distributes vertexes in a free space in a balanced way by ensuring that the lengths of edges are below an edge length threshold. An optimized path graph is extracted from the compact mesh. An iterative vertex pushing method is proposed to include important obstacle boundary edges in the path graph. Dijkstra's shortest path searching algorithm is used to search the shortest path in the path graph. Experimental results show that the path planning using the optimized path graph is an order of magnitude faster than the quadtree approach while the length of the path generated by the proposed method is almost the same as that of the path generated by the quadtree
Autonomous management of clustered server systems using JINI
No full textA framework for the autonomous management of clustered server systems called LAMA(1) (Large-scale system's Autonomous Management Agent) is proposed in this paper. LAMA is based on agents, which are distributed over the nodes and built on JINI infrastructure. There are two classes of agents: a grand LAMA and ordinary LAMAs. An ordinary LAMA abstracts an individual node and performs node-wide configuration. The grand LAMA is responsible for monitoring and controlling all the ordinary ones. Using the discovery,join, lookup, and distributed security operations of JINI, anode can join the clustered system without secure administration. Also, a node's failure can be detected automatically using the lease interface of the JINI. Resource reallocation is performed dynamically by a reallocation engine in the grand agent. The reallocation engine gathers the status of remote nodes, predicts resource demands, and executes reallocation by accessing the ordinary agents. The proposed framework is verified on our own clustered internet servers, called the CORE-Web server, for an audio-streaming service. The nodes are dynamically reallocated satisfying the performance requirements
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
SYNTHESIS OF ALKYLIDYNE COMPLEXES OF BR(CO)2(TMEDA)MCC6H4ME (M=CR, MO W) - CRYSTAL-STRUCTURE OF BR(CO)2(TMEDA)CRCC6H4ME
No full textThe reaction of (CO5)M=C(OMe)Tol (M=Cr, Mo, W and Tol=P-C6H4Me) and BBr3 followed by treatment with tetramethylethylenediamine (TMEDA) yields a mixture of two diastereomers, trans, cis-Br(CO)2(tmeda)M=CTol [M =Cr(1a), Mo(2a), W(3a)] and cis, trans-Br(CO)2(tmeda)M=CTol [M=Cr(1b), Mo(2b), W(3b)], respectively. These compounds have been isolated as crystalline solids and characterized by spectroscopic (infrared, mass, H-1 and C-13-NMR) data. The trans, cis-Br(CO)2(tmeda)Cr=CTol (1a), has been examine via a single crystal X-ray diffraction study: BrCrO2N2C16H23, Mr=407.27, triclinic, P1BAR, a=12.792(2), b=13.400(5), c=11.645(4) angstrom, alpha=101.26(2)-degrees, beta=103.04(2)-degrees, gamma=91.88(2)-degrees, V=1907(l) angstrom3, Z=2, rho(calcd)=1.418 gcm-3, lambda(MoKalpha)=0.71069 angstrom, mu=26.25 cm-1, F(000)=831.97, T=295 K, R=0.0977 for 1332 significant reflections [F(o)>5sigma(F(o))]. There are two essentially equivalent molecules in the crystallographic asymmetric unit. Each molecule is octahedral with the bromide ligand trans to the alkylidyne carbon, the two cis-carbonyl ligands, and the bidentate TMEDA ligand
CONSECUTIVE C-C BOND SCISSION OF AN ALLYL LIGAND ON A WOS3 CLUSTER FRAMEWORK
No full textThe reaction, of Os-3(CO)(9)(C(2)R(2)) (R = Tol, Ph; Tol = p-C(6)H(4)Me) with Cp(CO)(2)W=CTol (Cp = eta(5)-C5H5) produces an alkylidyne-alkyne complex CpWOs(3)(CO)(10)(mu(3)-eta(2)-C(2)R(2))(mu(3)-CTol) [1a (R = Tol), 1b (R = Ph)], which is converted to two isomeric allyl complexes CpWOs(3)(CO)(10)(mu(3)-C(3)R(2)Tol) (2a,b and 3a,b) upon thermolysis. Complexes 3a,b, in which the allyl ligand is pi-coordinated to the tungsten atom, undergo consecutive allyl C-C bond cleavage to afford trialkylidyne complexes CpWOs(3)(CO)(9)(mu(3)-CR)(2)(mu 3-CTol) (5a,b) via alkylidyne-alkyne complex CpWOs(3)(CO)(10)(mu(3)-eta(2)-C(2)R(2))(mu(3)-CTol) or CpWOs(3)(Co)(10)(mu 3-eta(2)-C(2)RTol)(mu(3)-CR) (4a,b), together with formation of CpWOs(3)(CO)(8)(mu(3)-perpendicular to-C(2)R(2))(mu(3)-CTol) or CpWOs(3)(CO)(8)(mu(3)-eta(2)-perpendicular to-C(2)RTol)(mu(3)-CR) (6a,b) as a minor product
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